Floral induction in tropical fruit trees: Effects of temperature and water supply

Summary

Floral induction in tropical trees generally follows a check in vegetative growth. However, it is not easy to identify the environmental factors involved in flowering, which normally occurs during the dry season when temperatures are also often lower. The separate and combined effects of temperature and water supply on floral induction were investigated in ‘Hass’ avocado (Persea americana), ‘Lisbon’ lemon (Citrus limon). ‘Wai Chee’ litchi (Litchi chinensis) and ‘Sensation’ mango (Mangifera indica). Low temperatures (15°/10°C or 15°/10°C and 20°/15°C compared with 30°/25°C and 25°/20°C) generally decreased vegetative growth and induced flowering in well-watered avocado, litchi and mango. A pre-dawn leaf water potential (ψ_L) of ?1.7 to ?3.5 MPa compared with ?0.4 to ?0.7 MPa in control avocado and litchi, and a pre-dawn relative water content (R.W.C.) of 90-93% compared with 97% or above in control mango plants also reduced or eliminated vegetative growth, but did not induce flowering. Low temperatures (15°/10°C compared with 20°/5°C, 25°/20°C or 30°/25°C) and water stress (pre-dawn ψ_L of ?2.0 to ?3.5 MPa compared with ?0.7 to ?0.8 MPa in controls) reduced or eliminated vegetative growth in lemon. In contrast to the response in avocado, litchi and mango, flowering in lemon was very weak in the absence of water stress at 15°/10°C or outdoors in Brisbane in subtropical Australia (Lat. 28°S), and was greatest after a period of water stress. The number of flowers increased with the severity and duration of water stress (two, four or eight weeks) and was generally greater after constant rather than with cyclic water stress. In lemon and litchi, net photosynthesis declined with increasing water stress reaching zero with a midday ψ_L of ?3.5 to ?4.0 MPa. This decline in carbon assimilation appeared to be almost entirely due to stomatal closure. Despite the reduction in midday CO₂ assimilation, starch concentration increased during water stress, especially in the branches, trunk and roots of lemon. Leaf starch was uniformly low. The number of flowers per tree in lemon was strongly correlated with starch in the branches (r²=77%, P<0.01) and roots (r²=74%, P<0.001). In litchi, starch was lower than in lemon roots and was not related to flowering.

In separate experiments to test the interaction between temperature and water supply, low day/night temperatures (23°/18° and 18°/15°C compared with 29°/25°C) reduced vegetative growth and induced flowering in avocado, litchi and mango. None of these species flowered at 29°/25°C or as a result of water stress (ψ_L of ?1.5 MPa compared with ?0.3 MPa for avocado and ?2.0 MPa compared with ?0.5 MPa for litchi, and R.W.C, of 90-93% compared with 95-96% in mango). In contrast, in lemon, flowering was very weak (<10 flowers per tree) in the absence of water stress (pre-dawn ψ_L of ?2.0 MPa compared with ?0.5 MPa) and was only heavy (>35 flowers per tree) after stressed trees were rewatered. There were slightly more flowers at 18°/15°C than at 23°/18° and 29°/25°C in control plants, but no effect of temperature in stressed plants. Starch concentration in the roots of avocado, lemon, litchi and mango was generally higher at 18°/15°C and 23°/18°C than at 29°/25°C. Water stress increased the starch concentration in the roots of lemon and litchi and decreased it in avocado. There was no effect in mango. There was a weak relation (r²=57%, P<0.05) between the number of flowers per tree in lemon and the concentration of starch in the roots. In contrast, there was no significant relationship between flowering and starch levels under the various temperature and water regimes in the other species. In another experiment, only vegetative growth in litchi and mango occurred at 30°/25°C and only flowering at 15°/10°C. Six weeks of water stress (pre-dawn ψ_L of ?2.5 MPa compared with ?1.0 MPa or higher in litchi, and R.W.C, of 90-93% compared with 95% or higher in mango) in a heated glasshouse (30°C days/20°C night minimum) before these temperature treatments did not induce flowering.

Temperatures below 25°C for avocado and below 20°C for litchi and mango are essential for flowering and cannot be replaced by water stress. The control of flowering in lemon over the range of day temperatures from 18°C to 30°C differed from that of the other species in being mainly determined by water stress. Flowering was generally weak in well-watered plants even with days at 18°C. Starch did not appear to control flowering.     

Regulated deficit irrigation in potted Dianthus plants: Effects of severe and moderate water stress on growth and physiological responses

The purpose of this study was to analyze the physiological and morphological response of carnation plants to different levels of irrigation and to evaluate regulated deficit irrigation as a possible technique for saving water through the application of controlled drought stress. Carnations, Dianthus caryophyllus L. cultivar, were pot-grown in an unheated greenhouse and submitted to two experiments. In the first experiment, the plants were exposed to three irrigation treatments: (control); 70% of the control (moderate deficit irrigation, MDI) and 35% of the control (severe deficit irrigation, SDI). In the second experiment, the plants were submitted to a control treatment, deficit irrigation (DI, 50% of the control) and regulated deficit irrigation (RDI). After 15 weeks, MDI plants showed a slightly reduced total dry weight, plant height and leaf area, while SDI had clearly reduced all the plant size parameters. RDI plants had similar leaf area and total dry weight to the control treatment during the blooming phase. MDI did not affect the number of flowers and no great differences in the colour parameters were observed. RDI plants had higher flower dry weight, while plant quality was affected by the SDI (lower number of shoots and flowers, lower relative chlorophyll content). Leaf osmotic potential decreased with deficit irrigation, but more markedly in SDI, which induced higher values of leaf pressure. Stomatal conductance (g_s) decreased in drought conditions more than the photosynthetic rate (P_n). Osmotic adjustment of 0.3 MPa accompanied by decreases in elasticity in response to drought resulted in turgor less at lower leaf water potentials and prevented turgor loss during drought periods.     

Effects of water stress and re watering on ribulose-1,5-bis-phosphate carboxylase activity,chlorophyll and protein contents in two cultivars of tomato

Summary

The effects of water deficit and rewatering on ribulose-1,5-bis-phosphate carboxylase activity, chlorophyll and protein content were evaluated in plants of two cultivars of tomato. During the water deficit period, values of water potential, osmotic potential and relative water content decreased along with associated decreases in RuBPcase activity, protein content and chlorophyll content, being less marked for chlorophyll content. There was a significant correlation of RuBPcase activity and protein content with components of leaf water status from plants under water stress. The associated decrease of RuBPcase, chlorophyll and protein contents with decreased osmotic potential during the development of water deficit was evident. At the time the plants reached a water potential of –1.40 to –1.56 MPa (RI: first level of recovery after water stress), one group of plants was rewatered. The rest were kept under stress until the water potential reached values of –2.30 to –2.51 MPa (RII: second level of recovery after water stress). It was observed that all of the varieties measured at both levels (RI and RII) showed a gradual recovery, reaching or even surpassing the values of control plants.     

Vascular blockage in cut roses in a suspension of Pseudomonas fluorescens

Summary

To analyse quantitatively the relationships between cut rose (Rosa hybrida L. ‘Pascha’) vase-life, the onset of cavitation, plant water potential, and bacterial concentrations in the vase water, rose stems were placed in water containing different concentrations of Pseudomonas fluorescens 2892 tet^r rif ^r. There was a significant correlation (P = 0.0009) between cut rose vase-life and the concentration of bacteria in the vase water. As the number of bacteria in the vase water increased, the rate of senescence also increased. The water potential for roses in the bacterial suspension (at 8.50 log₁₀ CFU ml^–1) proceeded to drop constantly after 5.17 h in the vase solution, with the water potential falling to as low as -2.35 MPa by the end of the experiment (at 117 h). In contrast, the water potential of roses in deionised water dropped from -0.419 MPa at 5.17 h, to only –0.663 MPa after 117 h. When roses were stood in a bacterial suspension (at 8.5 log₁₀ CFU ml^–1) for 30 h, 63.8% of the total cumulative cavitation events were seen, while roses stood in deionised water exhibited only 26.8% of the total cavitation events. Uptake of acid fuchsin and the movement of tagged P. fluorescens 2892 in the xylem indicated that bacteria did not travel beyond the open-ended xylem vessels and were generally restricted to the first 50 mm from the cut end of the stem.     

抗坏血酸提高月季切花失水胁迫耐性与增加APX活性的关系

 以‘Samantha’品种为试材, 确定了适宜的抗坏血酸(AsA) 预处理浓度, 探讨了AsA和抗坏血酸过氧化物酶(APX) 抑制剂(对氨基酚, β-aminophenol) 预处理对花瓣中相对电导率、AsA含量以及APX活性的影响。与未经失水胁迫的切花月季相比较, 失水胁迫处理抑制切花的开放进程, 缩短了瓶插寿命。AsA 1 000 mg·L ^{- 1}预处理可有效地改善花朵的开放状况, 显著降低花瓣中相对电导率的增加, 明显提高花瓣中AsA的含量和APX活性。500 mg·L ^{- 1} β-aminophenol预处理则起到相反的效应。结果说明,AsA对‘Samantha’月季切花失水胁迫耐性的改善与花瓣中APX活性的提高相联系。     

Phenology and drought affects the relationship between daily trunk shrinkage and midday stem water potential of peach trees

Summary

The relationship between maximum daily shrinkage in trunks (MDS), daily trunk growth (DTG), predawn water potential (Ψ_pd) and midday stem water potential (Ψ_stem) were studied in an irrigation experiment in peach trees. Control trees were irrigated to replace evapotranspiration, with trees receiving regulated deficit irrigation (RDI) watered at 35% of this rate during Stage II of fruit development and after harvest. The RDI trees were watered as controls during Stage III of fruit development. Minimum (Ψ_pd and Ψ_stem fell to –0.6.MPa and –1.2 MPa, respectively in RDI plots compared with –0.2 and –0.6 MPa in the controls. Trunk growth was less in the RDI plots than in the controls during drought. In contrast, MDS was higher when deficit irrigation was applied in the RDI trees. When site differences were considered the correlation between (Ψ_pd and accumulated trunk growth over an ample period was loose, while maximum daily shrinkage and midday stem water potential remarkably improved such a correlation. However, pooling all available data, the correlation between Ψ_stem and MDS was very poor (R²=0.44) and it substantially improved only when using data from specific phenological periods (i.e. R²=0.75). A seasonal drift in MDS values was observed and it was related to the seasonal changes in trunk growth rates, (i.e. highest shrinkage was found when growth rates were lowest). We concluded that phenology in combination with drought reduce the reliability of the water status information obtained from MDS.     

不同无土基质对微型盆栽月季生长发育的影响

 研究了7 种无土复合基质对微型盆栽月季( Rosa hybrida‘Miniature Pink’) 生长与发育的影响,结果表明, 100%泥炭、70%泥炭+ 30%珍珠岩、70%珍珠岩+ 30%泥炭3 种基质比较理想, 对其生长及开花均表现为显著的促进作用; 微型盆栽月季无土基质的优化物理性状为: 容重0.12～0.19 g·cm^-3 , 比重1.6～1.9 g·cm^-3 , 含水量(风干基质) 6%～16% , 总孔隙度90 %～94 %。     

Osmotic adjustment,proline accumulation and cell membrane stability in leaves of Cocos nucifera submitted to drought stress

The role of drought-induced proline accumulation in coconut leaves is still unclear. With the objective of evaluating the impact of water shortage on leaf osmotic potential, proline accumulation and cell membrane stability in young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting areas (Brazilian Green Dwarf from Una, Bahia, UGD, and from Jiqui, Rio Grande do Norte, JGD), a pot experiment was conducted under greenhouse conditions. Three drought cycles consisting of suspension of irrigation until the net photosynthetic rate (A) approached zero and rewatering until recovery of A to 85% of the irrigated control plants. Pre-dawn leaf water potential (Ψ_PD) reached −1.2 MPa at the point of maximum stress (PMS). Dry matter production and leaf area were severely reduced by drought treatment in the two ecotypes. Corrected values of osmotic potential were significantly reduced in stressed plants of the two ecotypes. Green dwarf coconut palm showed low osmotic adjustment (from 0.05 to 0.24 MPa) and significant accumulation of proline (from 1.5 to 2.1 times in relation to control) in leaflets in response to water deficit. Considering the growth reduction observed in both ecotypes, proline was not associated to osmoregulation. On the other hand, the absence of membrane damage, as indicated by electrolyte leakage method, suggests that the protective role of proline in this specie can be more important. The two ecotypes of Green dwarf coconut palm behaved similarly in the present experiment for most traits evaluated. Slight differences among the ecotypes were observed with respect to the response to treatments, such as higher proline accumulation in JGD.     

Productivity of olive trees with different water status and crop load

SUMMARY

A field experiment was conducted over two growing seasons to determine the combined effect of crop load and irrigation on yield components of olive trees (Olea europaea L. ‘Leccino’) planted at 6 m 3.8 m in a sandy-clay soil. Different crop loads were established by manual thinning of fruits. Drip irrigation was managed to maintain pre-dawn leaf water-potentials (PLWP) within the following ranges: (i) higher than –1.1 MPa (FI; fully irrigated); (ii) between –1.0 and –3.3 MPa (DI; deficit irrigated); or (iii) below –1.2 MPa, but not lower than –4.2 MPa (SI; severe deficit irrigated). The irrigation period lasted from 6 – 16 weeks after full bloom (AFB) in 2003, and from 5 – 19 weeks AFB in 2004. In 2003, full bloom was on 26 May; in 2004, it was on 3 June. Neither irrigation regime nor crop load affected flowering or flower quality the following Spring. The combined fruit yields [on a fresh weight (FW) basis] over both years in SI and DI trees were 49.0% and 81.6% of FI trees, respectively. The oil yields of SI and DI trees were 52.5% and 81.2% of FI trees, respectively. Fruit FWs in FI trees were greater than those of DI or SI trees at 8 weeks AFB. At harvest, FI trees bore the largest fruits, and SI trees the smallest fruits. The FWs of individual fruits at harvest in the FI and DI treatments decreased as crop load increased, but no such relationship was apparent for SI trees. The oil content of the mesocarp increased as PLWP increased from approx. –3.5 MPa to –1.5 MPa. The oil content of FI trees at harvest decreased from 53.1% to 45.7% dry weight as fresh fruit yield increased from 5 – 25 kg dm^–2 trunk cross-sectional area. However, crop load did not have any effect on the oil content of the mesocarp in DI trees. Fruit maturation was delayed by irrigation. Maturation index also decreased (indicating delayed maturation) as the crop load on FI or DI trees increased, but did not vary with crop level in SI trees.     

葡萄试管苗不同叶位叶片光合与呼吸的特性

 用CIRA - 2 型光合测定仪, 采用密闭系统落差法测定‘红地球’葡萄试管苗不同叶位的净光合速率(Pn) 和呼吸速率(Rd) 。结果表明, 葡萄试管苗具有一定的光合能力, Pn 值随叶位的升高而降低, Rd 随叶位的升高而升高, CO₂浓度的升高具有提高叶片光合速率和抑制呼吸作用的双重作用。随光强度的增大, 叶片的光合能力明显提高; 随温度的升高, 叶片的Rd 均呈上升趋势, 但Pn 呈现出先升后降的趋势。不同叶位的CO₂补偿点随温度的升高而提高。     

温度和光照对‘红地球’葡萄试管苗光合特性的影响

 以‘红地球’葡萄(Vitis vinifera L. ‘Red Globe’) 试管苗为试材, 采用密闭系统落差法研究了在不同温度和光照强度下培养28 d的试管苗的光合特性。结果表明: 培养温度在20～30 ℃之间, 试管苗的暗呼吸速率(Rd ) 随温度的升高而升高, 但净光合速率( Pn ) 以25 ℃最高, 30 ℃次之, 20 ℃最低;而CO₂补偿点以25 ℃最低, 20 ℃次之, 30 ℃最高; 光照强度在40～200μmol·m ^-2 ·s^-1之间, 葡萄试管苗的P_n随光照强度( PAR) 的升高而升高, CO₂补偿点随PAR的升高而降低。在光照条件下, 容器内CO₂浓度迅速降低, 并接近CO₂补偿点, CO₂供应不足是影响试管苗同化能力的主要原因。在室内培养阶段,采用弱光、昼夜变温和改善培养容器的通气性有利于提高试管苗的光合能力; 在移栽驯化过程中, 逐步提高光照强度和延长光照时间有利于试管苗同化产物的积累和培养壮苗。     

Photosynthetic responses of greenhouse tomato plants to high solution electrical conductivity and low soil water content

SUMMARY

Greenhouse tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in a peal-moss based substrate and supplied with nutrient solutions of high (4.5 mS cm^-1) or low (2.3 mS cm^-1) electrical conductivity (EC) and under high (95 ± 5%) or low (55 ± 8% of capillary capacity) soil water content, to elucidate how EC and soil water status affect plant photosynthesis and related physiological processes. Two weeks after beginning the treatments, photosynthesis (Pn) was measured during changes of photo-synthetic photon flux (PPF) from 0 to 1200 u.mol m^-2 s^-1 using a gas exchange method. The rectangular hyperbolic model (Pn = P_max KI (1-KI)^-2 -r) provided a good fit for the photosynthetic light-response curve. High EC treatment changed the curve by increasing the initial slope (quantum yield) and decreasing photosynthetic capacity at high PPF. However, soil water deficit not only decreased the photosynthetic capacity, but also decreased quantum use efficiency. Depression of Pn was attributed to decreased stomatal (gs) and mesophyll (_gm) conductances, but g_s was depressed more than g_m. The ratio of _gm/(g_m + g_s), an indicator of water use efficiency and a measure of relative control of Pn by carboxylation and C02 supply, was higher for high-EC treated plants. Chlorophyll content was increased by high EC treatment, and was consistent with quantum yield. Leaf water potential was decreased by high EC and/or low soil water content and the decreases in leaf water potential ultimately accounted for the Pn depressions. The effects of high EC and soil water deficit were additive on photosynthesis and most related physiological processes.     

谷胱甘肽提高月季切花失水胁迫耐性与GR活性的关系

 本研究确定了切花月季‘Samantha’预处理采用的谷胱甘肽(GSH) 及其生物合成抑制剂丁胱亚磺酰胺〔L-buthione (S, R) sulfoximine, BSO〕适宜浓度, 探讨了GSH和BSO预处理对花朵水势、花瓣中MDA含量、GSH含量以及GR活性等的影响。结果表明: 与失水胁迫对照处理相比较, 2 mmol/L GSH预处理明显提高了月季切花瓶插期间花朵水势, 显著降低了花瓣中MDA含量, 有效提高了花瓣中GSH含量和GR活性。2 mmol/L BSO预处理获得了理想的反证结果。结果说明, GSH对切花月季‘Samantha’失水胁迫耐性的改善与花瓣中GR活性的提高相联系。     

The role of calcium in regulating photosynthesis and related physiological indexes of cucumber seedlings under low light intensity and suboptimal temperature stress

The response of photosynthesis, antioxidant enzyme activity, and proline content to low light intensity and suboptimal temperature in Cucumis sativa L. seedlings pretreated with either distilled water, 10 mM CaCl₂, 1 mM LaCl₃, 3 mM ethyleneglycol-bis-(2-aminoethyl) tetraacetic acid (EGTA) or 0.05 mM chlorpromazine (CPZ) were investigated. The results showed that 10 mM CaCl₂ led to an increase in photosynthetic rate (Pn), carboxylation efficiency (CE), ribulose 1,5-biphosphate carboxylase (RuBPCase) activity, chlorophyll content, peroxidase (POD) and catalase (CAT) activity, and proline content of cucumber seedlings under low light intensity and suboptimal temperature, in comparison with the distilled water-pretreated seedlings. However, LaCl₃, EGTA and CPZ were in contrast to CaCl₂. These results suggest that CaCl₂ has beneficial effect on photosynthetic adaptation to low light and suboptimal temperature stress in cucumber seedlings. This might be related to the observed increase in RuBPCase activity, alleviation of lipid peroxidation and enhancement of osmoregulation, with these effects being inhibited by LaCl₃, EGTA and CPZ.     

Effect of pruning and plant spacing on the growth of cherry rootstocks and their influence on stem water potential of sweet cherry trees

Summary

The aims of this work are to describe the effects of pruning and planting density on growth and water relations of ungrafted and grafted sweet cherry trees. A trial with cherry rootstocks ‘Prunus avium’, ‘CAB 11E’, ‘Maxma 14’, ‘Gisela 5’ and ‘Edabriz’ was begun in 1997. Pruning severities were applied to the rootstocks (0, 30, 60 and 90% of the vegetative growth was removed corresponding to P1, P2, P3 and P4 treatments, respectively) after planting to two plant spacings (S1 = 0.25 × 1.0 m and S2= 0.45 × 1.5 m). Canopy, root growth and leaf water potential (ψ_leaf) were quantified throughout the growing season. Pruning significantly affected root length and root weight of the rootstocks. Uncut plants (P1) showed a heavier and expanded root biomass (231 g and 108 m) than the intensively pruned plants (P4) (187 g and 75 m). The greater root biomass was obtained with the spacing/pruning combination, S1/P1 (285 g), and the smaller with S1/P4 (180 g) and S2/P4 (176 g). ψ_leaf varied significantly between the rootstocks and plant spacing but not with pruning. ‘Maxma 14’ and ‘P. avium’ attained the lowest values of midday ψ_leaf, –2.28 and –2.04 MPa, but the highest values of predawn ψ_leaf, –0.29 and –0.25 MPa, respectively. Generally, with high density (S1), the rootstocks exhibited lower predawn and midday ψ_leaf. In 1998, cultivars ‘Burlat’, ‘Summit’ and ‘Van’ were grafted onto rootstocks and a trial was installed in 1999. Predawn and midday stem water potential (ψ_stem) on cherry trees, measured in 2002, were affected significantly by the rootstock/genotype combination. Cultivars grafted on ‘P. avium’ and ‘Maxma 14’ showed the less negative midday ψ_stem, –1.36 and –1.42 MPa respectively, so these rootstock genotypes perhaps induced a higher drought resistance to the scion. Recorded data show that the scion-rootstock interaction with regard to production performance under water deficits may be an important consideration in cherry tree planting strategies.     

The effect of irrigation and crop load on stem water potential and apple fruit size

Summary

The effect of irrigation rate under various crop loads on the fruit size of apple (Malus domestica Borkh cv. Golden Delicious) was investigated in three field experiments in 1993–1995. During the first two years the field experiments evaluated the effects of various crop loads on yield, fruit size and midday stem water potential under 40% deficit irrigation. In 1995, the effects of five irrigation levels (0.42–1.06 of USDA Class A evaporation pan) and four crop loads (100–450 fruits per tree) were studied in a factorial experiment. Midday stem water potential increased with irrigation level and decreased with crop load in 1993 and at the lowest irrigation level in 1995. Daily fruit growth rate decreased with midday stem water potential in 1993 and at the lowest irrigation level in 1993. The effect of crop load on fruit growth rate was associated with limited soil water availability. A reduction in yield and average fruit size were associated with midday stem water potentials lower than –1.3 MPa. Taking an additional 0.1 MPa as a safety factor, –1.2 MPa could serve as a reasonable threshold for irrigation control in the orchard.     

Photosynthetic characteristics of highbush blueberry (Vaccinium corymbosum cv. Bluecrop) leaves in response to water stress and subsequent re-irrigation

SUMMARY

Gas exchange and photosystem II (PSII) activities in the leaves of 2-year-old ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) were monitored during water stress and subsequent re-irrigation to investigate the effects of the intensity of water stress on changes in photosynthetic characteristics. The blueberry shrubs were not irrigated for 3 to 5 weeks, then re-irrigated daily up to 8 weeks. The decrease in soil water potential during water stress caused a progressive decrease in leaf water potential. Soil water potentials decreased to -0.26 MPa and -0.34 MPa at 3 and 5 weeks, respectively, following water stress, but recovered following subsequent re-irrigation, while the soil water potential in daily-irrigated shrubs was maintained at over -0.13 MPa throughout the experiment. Chlorophyll concentrations decreased with an increasing duration of water stress. Chlorophyll concentrations in leaves on shrubs subjected to water stress for 5 weeks did not recover following re-irrigation, unlike those subjected to water stress for 3 weeks. The leaves on shrubs subjected to water stress for 5 weeks maintained lower levels of chlorophyll during reirrigation. The net rate of CO₂ assimilation (A_n) decreased significantly with an increasing duration of water stress. Reirrigation reversed the decrease in A_n in leaves on shrubs subjected to water stress for 3 weeks. Stomatal conductance (g_s) exhibited a similar pattern to A_n. The actual quantum yield of photosystem II (Φ_PSII) and the electron transport rate (ETR) also decreased significantly with an increasing duration of water stress, although the F_v/F_m ratio was not affected. Φ_PPSII and ETR values in the leaves on shrubs subjected to water stress for 5 weeks did not recover after reirrigation, unlike those subjected to water stress for 3 weeks. Non-photochemical quenching increased with an increasing duration of water stress, but subsequent re-irrigation did not reverse the increase. These results indicate that the timing of re-irrigation of water-stressed ‘Bluecrop’ highbush blueberry is critical in order to maintain their photosynthetic capacity. Among the photosynthetic characteristics measured, Φ_PSII and ETR could be used as sensitive indicators to assess the physiological status of leaves of ‘Bluecrop’ highbush blueberry growing under water stress conditions.     

Effect of green tea extract powder on the vase-life of fresh-cut rose (Rosa hybrida L.) ‘Carola’ stems

To develop an innocuous, easy-to-use, and inexpensive preservative for the cut flower industry, green tea extract (GTE) powder was applied in the fresh-cut rose stem preservation process to exploit its high anti-oxidative and anti-microbial properties. The effects of 2.0 g l^?1 GTE powder in the vase solution on the vase-life and flowering profile of cut rose (Rosa hybrida ‘Carola’) stems were investigated. The effectiveness of GTE powder was also compared with other preservatives such as 2% (w/v) sucrose, 200 mg l^?1 8-hydroxyquinoline citrate plus 2% (w/v) sucrose, or 0.2 mM silver thiosulphate in the vase solution, with distilled water as a control. The results showed that, compared to the control, the 2.0 g l^?1 GTE powder treatment extended the vase-life and reduced the loss in fresh weight in cut rose stems in the vase solution. GTE at 2.0 g l^?1 provided the highest anti-bacterial activity (4.2 log₁₀ CFU ml^?1 on day-6) and prevented the decline in anthocyanin concentrations compared to that seen in the control stems, suggesting that GTE powder could be used as a preservative to extend the vase-life of fresh-cut rose flowers.     

Involvement of proline in response of chickpea (Cicer arietinum L.) to chilling stress at reproductive stage

Chickpea is sensitive to chilling stress, especially at its reproductive stage and experiences abortion of flowers and poor pod set at temperatures below 10 °C. The metabolic controls governing chilling-sensitivity in chickpea, particularly involving proline are not known. Hence, in the present study we explored the role of proline in this regard. A set of chickpea plants (cv. GPF2) growing under warm conditions of the glass house (temperature – 28/14 °C as average maximum and minimum till early flowering stage) was exposed to low temperature conditions of the field (8.3–9.6/2.8–5.3 °C; average maximum and minimum temperature, respectively) during the onset of reproductive phase while another set of plants continued to grow under warm conditions. In case of chilling-stressed plants, one set of the plants was treated with 10 μM proline while the other set not treated with proline served as control under low temperature conditions. In untreated chilling-stressed plants, the endogenous proline increased to 230 μmol g⁻¹ dry weight (DW) on 4th day of stress and decreased thereafter to reach 28 μmol on 7th day. In plants treated with 10 μM proline, its endogenous content reached 310 μmol g⁻¹ DW on 4th day and stayed significantly higher than untreated chilling-stressed plants. The proline-treated plants showed significant improvement in retention of flowers and pods leading to better seed yield compared to the untreated ones. The proline-applied plants also had greater pollen viability, pollen germination, pollen tube growth and ovule viability. The stress injury measured as oxidative stress, electrolyte leakage, loss of chlorophyll and decrease in leaf water content was mitigated significantly in proline-treated plants. Additionally, proline application increased the level of sucrose and trehalose (cryoprotectants) in chilling-stressed plants. The studies revealed that proline application was significantly effective in reducing the impact of chilling injury on reproductive growth in chickpea.     

Acetyl salicylic acid induces stress tolerance in tomato plants grown at a low night-time temperature

Summary

Abiotic stresses are becoming more prevalent as the intensity of agriculture and the demand for farmable land increase. Night-time temperature is one of the major environmental factors that influence plant metabolic processes. The permeability of cell membranes, levels of osmoregulatory substances, reproductive flowering stage, growth rate, and total anti-oxidant capacities of leaves were investigated in tomato (Solanum lycopersicum, formerly Lycopersicon esculentum Mill. ‘Liaoyuanduoli’) plants exposed to a low night-time temperature (LNT) of 9ºC or to an ambient night-time temperature (ANT) of 15ºC, with or without exogenous foliar spray treatment with acetyl salicylic acid (acetyl-SA). Three applications of 1.0 ml of 0.4 mM acetyl-SA made to 4-week-old tomato seedlings at 5 d intervals reduced the decline in fruit yield in the first and second fruit clusters due to LNT treatment by decreasing malondialdehyde (MDA) and increasing proline concentrations and total anti-oxidant capacity in tomato leaves. Under LNT stress, lipid peroxidation, measured in terms of MDA content, and hence membrane permeability were reduced by 0.4 mM acetyl-SA treatment. Superoxide dismutase (SOD) and peroxidase (POX) activities were increased by 0.4 mM acetyl-SA treatment. The accumulation of superoxide free radicals (O₂ ^?–) was inhibited, but H₂O₂ concentrations were increased by 0.4 mM acetyl-SA treatment. These results suggest that acetyl-SA could be used as a growth regulator to improve fruit yields and the tolerance of tomato plants exposed to LNT stress.