Plant Responses to Water Stress

This Special Issue comprises a series of papers that developsthe theme of plant responses to water stress, encompassing recentdevelopments at the molecular level, through responses of photosynthesisand metabolism, to their application in crop selection and yield.The consideration of water deficits is particularly timely,given the huge developments in this area in the past decade.This issue specifically sets out to place molecular and physiologicalprocesses and their agronomic applications in an environmentalcontext.     

The fine structure of autotrophic and heterotrophic cells of Chlorella vulgaris (Emerson strain)

Cells of the Emerson strain of Chlorella vulgaris become verymuch enlarged when cultured heterotrophically. The ultrastructureof these giant cells has been examined and compared with thatof cells cultured autotrophically. The chief area of differenceis within the chloroplast where there is a massive accumulationof starch and little or no synthesis of lamellae under heterotrophicconditions. Synthesis of cell wall material is apparently possibleunder heterotrophic conditions but the production of the variouscellular organelles does not keep pace with the increase incell volume. (Received August 12, 1968; )     

Development of pepper (Capsicum annuum) seed quality

Changes in seed quality in pepper (Capsicum annuum L.) were monitored during seed development and maturation in two seasons. Seed quality was assessed by a number of different tests, but principally by determining seed storage longevity in laboratory tests and seedling growth in glasshouse tests. Mass maturity (defined as the end of the seed-filling phase) occurred 49–53 days after anthesis (DAA) in 1989 (varying among fruit layers) and 53 DAA in 1990 when seed moisture contents were 51–53%. The onset of both germinability and desiccation tolerance occurred either just before or at mass maturity. Maximum potential longevity (assessed by the value of the seed lot constant K_i) was achieved 63–65 DAA, i.e. not until 10–12 days after mass maturity (DAMM), in both years. Seedling dry weights in the glasshouse growth tests were maximal later still - for seeds harvested 17–21 DAMM in 1989 and 17 DAMM in 1990; the effects on seedling weight arose from differences in times from sowing to emergence (P < 0.005) among different seed harvests, with no significant differences in subsequent relative growth rates (P > 0.25). Seed priming reduced mean germination times for seeds harvested at all stages of development, but had little effect on germination capacity and potential longevity, and did not affect the pattern of changes in potential longevity during seed development and maturation. The results contradict the hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline immediately thereafter.