Etiolated growth in relation to energy reserves and winter survival in three temperate grasses |
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Authors: | Masahisa Moriyama Jiro Abe Midori Yoshida |
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Institution: | (1) National Agricultural Research Center for Hokkaido Region, Toyohira-ku Hituzigaoka 1, Sapporo 062-8555, Japan |
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Abstract: | The role of energy reserves in development of winter hardiness was examined in timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.) and perennial ryegrass (Lolium perenne L.) through periodically measuring etiolated growth (EG; shoot growth of crown under dark, warm and humid conditions following
defoliation) and determining sugar profiles at critical stages of hardening and wintering. Seasonal changes in weight and
duration of EG were monitored by sampling once or twice a month from September to the following April. In all species, total
etiolated growth (TEG; total shoot production at each sampling time as determined by weekly or biweekly harvests until exhaustion
of reserves) increased from September to reach peak levels during the second hardening stage in mid-November. Thereafter,
TEG remained high until the following spring in orchardgrass while it declined linearly in timothy,
which had the lowest TEG. The decline in TEG was intermediate in perennial ryegrass. Changes in the duration of EG were most
marked in orchardgrass, as it required six weeks to produce about 150 mg g-1 TEG in early November but only one week in March. The results indicated occurrence of dormancy in apical meristems of orchardgrass
at the end of the first hardening stage with temperatures above 0 °C, which roughly corresponded with the phase of dormancy in woody plants. Dormancy was weak in timothy and largely undetectable
in perennial ryegrass, as measured by the EG technique. A positively significant correlation between total nonstructural carbohydrates
(TNC) content and TEG was found in all species. Detailed analysis, however, showed that direct estimation of TNC content using
TEG was difficult because TEG production per unit TNC was negatively correlated with TNC level, and the amount of TNC unused
in early autumn was more than in the rest of the season. Changes in sugar profiles occurred at transition from the first to
the second hardening stage with subzero temperatures and varied with wintering strategy of each species. Simple sugar content
dramatically declined while fructan content increased in both timothy (cv. ‘Senpoku’) and orchardgrass (cv. ‘Wasemidori’),
which were selected at sites covered with snow for more than 120 days. In contrast, a cold tolerant perennial ryegrass cv.
`‘éveille’ selected in the Netherlands retained high amounts of simple sugars. The results suggest that EG technique is suitable
to monitor physiological status (amount and rate of mobilization of energy reserves, intensity of dormancy and bud development)
of plants expressing winter hardiness.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | carbohydrate dormancy etiolated growth freezing tolerance temperate grasses winter hardiness |
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