The path from β-carotene to carlactone, a strigolactone-like plant hormone

Strigolactones, phytohormones with diverse signaling activities, have a common structure consisting of two lactones connected by an enol-ether bridge. Strigolactones derive from carotenoids via a pathway involving the carotenoid cleavage dioxygenases 7 and 8 (CCD7 and CCD8) and the iron-binding protein D27. We show that D27 is a β-carotene isomerase that converts all-trans-β-carotene into 9-cis-β-carotene, which is cleaved by CCD7 into a 9-cis-configured aldehyde. CCD8 incorporates three oxygens into 9-cis-β-apo-10'-carotenal and performs molecular rearrangement, linking carotenoids with strigolactones and producing carlactone, a compound with strigolactone-like biological activities. Knowledge of the structure of carlactone will be crucial for understanding the biology of strigolactones and may have applications in combating parasitic weeds.     

Institutional support and in situ conservation in Mexico: biases against small-scale maize farmers in post-NAFTA agricultural policy

One of the major adjustments brought on by the North American Free Trade Agreement (NAFTA) was a change in the relationship between Mexican agricultural support institutions and the small-scale agricultural sector. Post-NAFTA restructuring programs sought to correct previous inefficiencies in this sector, but they have also had the effect of marginalizing the producers who steward and manage the country’s reserve of maize (Zea mays) genetic diversity. Framed by research suggesting that certain maize varieties in a rain-fed farming region in southern Sonora are in danger of loss due chiefly to long-term drought, this article explores the ramifications of post-NAFTA agricultural policies for in situ maize diversity conservation. Qualitative methods, including semi-structured interviews with agricultural support institutions and participant observation with farmers, were used to gather data on dryland farmers’ access to research and extension, as well as possibilities for collective action. In southern Sonora, agricultural support is oriented primarily toward high-tech production, and there are structural barriers to small-scale farmers’ access to research and extension institutions. Further, collective action around agriculture is limited. These circumstances represent significant limitations to farmers’ options for accessing new techniques which might help maintain maize diversity in the context of economic and environmental change.     

COMPARATIVE FEEDING VALUE OF SILAGES MADE FROM WILTED AND UNWILTED GRASS AND GRASS/CLOVER HERBAGE

Silage was made from wilted and unwilted grass in May 1965, 1966 and 1967. The silage was made in sealed silos, but these were not evacuated and additives were not used.
The silages were fed as follows: in 1965 to milking dairy cows and 1-year-old beef steers; in 1966 to steers coming into the experiment at 3, 9 and 15 months of age; in 1967 to weaned steer calves, with or without rolled barley (1 or 2 kg/head per day). In all years the silages were of high in vivo digestibility. The intake of wilted silage was higher than that of unwilted silage. There was no significant difference between the milk yields of cows fed on wilted and unwilted silage only. Liveweight gains were higher with wilted silage in 1965 and 1966, but not in 1967. In 1966 gains increased with age of animal and in 1967 gains were higher at successively higher levels of concentrate feeding.     

Inactivation of deltamethrin on stored wheat

Residues of deltamethrin on wheat grain of 12% moisture content, stored in the laboratory at 25°C, remained constant within experimental error over a 15-month interval. However, the biological activity of the residues against Sitophilus oryzae (L.) declined to 78% of the initial value at 3 months, and to 65% at 15 months after application. Inactivation of a proportion of the intact residues is indicated.     

COMPARATIVE STUDIES OF PERENNIAL RYEGRASS, TIMOTHY AND MEADOW FESCUE

The growth of calves grazing pure swards of perennial ryegrass, timothy and meadow fescue at low grazing pressure was measured. Organic-matter intake was estimated on three occasions during the grazing season. In 1963 rest periods of 7 days in April and May and of 21 days in June-Octoher were used hetween 7-day grazing periods. In 1964 the effect of long (35–55 days) and short (15–25 days) rest periods hetween 3.5-day grazing periods were compared. There were no measurable differences in intake hetween the calves on the three grass species in 1963. In 1964 faecal production was higher with timothy than with the other species and with small differences in digestihility, the intake on this species was higher. The faecal production and intake were higher, hut not significantly so, with the long-rest management in the second year. The liveweight gains of the calves grazing the three species were similar in 1963; in 1964 gains with meadow fescue were lower than with the other species from 13 April to 22 June but this was the only significant difference. The results obtained on slaughtering the calves at the end of each summer are presented.     

A COMPARISON OF THE PRODUCTIVITY OF ABERYSTWYTH-BRED AND COMMERCIAL GRASS VARIETIES IN SMALL FARM UNITS

A comparison of Aberystwyth-bred and commercial grass varieties on two small farms of approximately 17 acres was started in April 1958. The 10 plots comprising each unit are scattered in pairs over a total area of 35·5 acres [used from 1951 for a grazing management experiment (1, 2)]. The management and results for the first three years are given in this paper.
Varieties for both long- and short-term leys were compared; the re-seeding plan and seeds mixtures used are detailed. The stock numbers, grazing management and fertilizer treatments were kept as nearly similar as possible for the farms and for the individual mixtures. Figures for utilized herbage production from individual plots, assessed from grazing data and from sample cuts taken during silage and hay making, are discussed in relation to botanical composition. The levels of production are given in terms of utilized starch equivalent, live-weight gain, wool from the ewes and cattle grazing days. All show consistent differences in favour of the Aberystwyth-bred varieties, but mask a difference in favour of Danish compared with S37 cocksfoot.     

THE EFFECT OF LEVEL OF NITROGEN FERTILIZER ON BEEF PRODUCTION FROM GRAZED PERENNIAL RYEGRASS/WHITE CLOVER PASTURES

In a 3 × 3 factorial experiment, the effects of three levels of nitrogenous fertilizer (0, 336 and 672 kg/N per ha) and three grazing intensities on live-weight gains and carcass attributes were measured.
The live-weight gains of the animals (per head) over the season were greater at the low and moderate grazing intensities than at the high; this effect occurred mainly from July to October each year. Gains were low on the no-nitrogen swards from July 1962 to the end of the grazing season and throughout 1963: this was related to the very high clover content of the swards.
In all years, as grazing intensities increased, the carcass weights per animal became lower. Carcass balance, carcass length, depth of longissimus dorsi muscle, fat thickness over the longissimus dorsi, weight of kidney suet and channel fat, and weight of the alimentary tract also reflected the effect of treatment on weight gains.
The results are discussed in relation to the botanical composition and consumption of the herbage, presented in Part I.     

THE EFFECTS OF LEVEL OF NITROGEN FERTILIZER ON BEEF PRODUCTION FROM GRAZED PERENNIAL–RYEGRASS/WHITE–CLOVER PASTURES

The treatments in this summer–grazing experiment were designed as a 2 × 3 factorial, there being two levels of nitrogenous fertilizer (nitro–chalk), supplying 0 and 336kg of N/ha per annum (NO and N3, respectively) and three stocking rates. The fertilizer was applied in 7 dressings at approximately three–weekly intervals. The animals used were Hereford x Friesian steers; these were slaughtered at the end of the grazing season. The stocking rates were calculated on the basis of expected herbage production. The experiment was laid out in 6 randomized blocks which were grazed in rotation. Two blocks were cut for conservation before grazing each year; up to the end of June only 4 blocks were used for grazing.
There was little contamination of the swards with unsown species. With the NO swards the clover contents declined each year, but remained fairly high at over 20% in 1965. Clover contents also declined each year in the N3 swards and by 1965 were only 2 to 4%.
The quantities of herbage cut for conservation were higher from the swards receiving N. The live–weight gains of the cattle (per head) were higher at the lower stocking rates, the effect of stocking rate being more noticeable in the July to Oct. period. Live–weight gains per ha increased at the higher stocking rates. In 1963 and 1965, as stocking rates increased carcass weights per animal decreased and carcass quality, as indicated by the commercial grades, was poorer. In 1964, a dry spell from July to Oct. necessitated the removal of cattle from the experiment and the effects of treatment on carcass weight and quality were not apparent.