Effect of Altered Sink: Source Ratio on Photosynthetic Metabolism of Source Leaves

Abstract

ABSTRACrWhen seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Rapwaaus sativus L, but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of '4C detected in sugar phosphates and UDPglucose following '4CO2 supply.When mannose was supplied to leaf discs to sequester cytoplasmic inoranic phosphate, promotion of starch synthesis, and inhibition of C02 fixation, were observed in control discs, but not in discs from treated plants. Phosphate (Ricinus communis L.) were grown in 2-L cylindrical plastic containers filled with vermiculite. Plants were thinned to one plant per pot shortly after emergence and irrigated twice a week with deionized water and once a week with half-strength Hoagland solution. Excess water and solution were drained through the bottom ofthe container. All species were grown in a chamber maintained at 25C, at a quantum flux density of 450 ,umol m-2 s-' (400-700 nm) and a 13 h/l l h light/dark photoperiod.Experiments with cotton were conducted about 10 d after the appearance of the first flower (11-12 weeks after emergence). Bean plants were used at the stage of the fully expanded first trifoliate leaf (22-25 d after emergence).One experiment with cotton ( Fig. 1) was conducted on field grown plants, Cotton was planted on May 25 in rows 1 m apart and thinned to 10 plants/m2 after emergence. Following light sprinkling to ensure emergence, a trickle irrigation system was installed. Laterals were located next to plant rows and emitters were 40 cm apart. The plants were irrigated once a day and the quantity of water supplied was based on evaporation from a Class A pan. Nutrients containing urea, H3PO4 and KCI at N:P:K ratio of 4:1:2 were predissolved in the irrigation water at a concentration of 80 g x m-3. Plants were used for this experiment on August 12, when there were about 10 bolls or flowers per plant.The sink removed in the case of the growth-chamber grown cotton was the developing first boll, and measurements were conducted on the mature leaf adjacent to this boll peduncle. In the field-grown cotton, various numbers of boils or flowers were removed, and measurements were conducted on four leaves of different ages along the plant axis. The extracts of these were combined. In the case ofbean plants, the sink removed included the young developing second trifoliate leaf and developing buds. The first trifoliate leaf was considered as the source leaf.CO2 fixation rate was measured in 1.5 cm2 circular areas of attached leaves according to a procedure described earlier (12).

The respiratory energy requirements involved in nocturnal carbohydrate export from starch-storing mature source leaves and their contribution to leaf dark respiration

“…Nocturnal carbohydrate export rates (Ce; nmol sucrose m-2 s-1 ) were determined on bean leaves, which accumulate significant amounts of starch (Plaut et al, 1987). Our treatments to manipulate carbohydrate export rates were insufficient to obtain a range suitable for estimating Ee.…”

Photosynthetic Decline from High Temperature Stress during Maturation of Wheat

“…Source and sink activities are related by direct feedback mechanisms (16) during normal monocarpic senescence and by pathways in source tissue that mitigate effects of feedback regulation (5). Effects of stress on feedback regulation depend partly on relative sensitivity of source and sink activities to the stress.…”

Expression of Carotenoid Pathway Genes in Three Capsicum Varieties under Salt Stress

“…Earlier reports on the expression pattern of carotenoid pathway genes have been targeted on flower and fruit part but very scanty information is available in leaves (Plaut et al, 1987;Babu et al, 2011). Our data clearly show that a transcript of selected genes (PSY, PDS, ZDS, LYC-β and CCS) were detectable in leaf samples of all capsicum varieties (Romer et al, 1993).…”