Showing papers in "Plant and Cell Physiology in 1986"

Light Harvesting and Utilization by Phytoplankton

Abstract: Application d'un modele theorique a l'analyse des relations photosynthese-irradiance chez 3 especes marines phytoplanctoniques

Triadimefon Protects Bean Plants from Water Stress through its Effects on Abscisic Acid

Abstract: Examen des effets du triadimefon sur la croissance, les relations hydriques et les types de variations des teneurs en ABA en conditions de deficit hydrique

Effect of temperature on photosynthetic activities of senescing detached wheat leaves

Abstract: Changes in various components of photosynthetic activity during the dark induced senescence of detached wheat leaves, maintained at 25°C (control) and 35°C (mildly elevated temperature treatment), were examined. Senescence-associated decline measured up to 96 h, in photosynthetic activity was appreciably hastened at 35°C, than at 25°C as evident by the relative higher losses of chlorophyll, photosystem (PS) II and PS I catalyzed photochemical activities and ribulose-1,5-bisphosphate (RuBP) carboxylase activity. In addition, a comparatively higher rise in light scattering profile of isolated chloroplasts was noted at 35°C than at 25°C. Senescence-induced degradation of chlorophyll was faster at 35°C than at 25°C; on the other hand, the degradation of carotenoids was faster at 25°C than at 35°C. Furthermore, the ratio of carotenoids to chlorophyll increased with senescence up to 96 hours, higher ratio being obtained at 35°C than at 25°C. Both PS II and PS I activities showed a transient rise in the beginning phase of dark incubation, whereas loss in chlorophyll was continuous throughout the period of senescence. The initial rise observed in photochemical activities was attributable to the uncoupling of electron transport from photophosphorylation. Elevated temperature treatment resulted in greater inactivation of RuBP carboxylase than control. It appears that during senescence the loss in chlorophyll and RuBP carboxylase activity are triggered simultaneously.

Behavior of Chloroplast Nucleus during Chloroplast Development and Degeneration in Chlamydomonas reinhardii

Abstract: Changes in morphology of chloroplast nuclei (cp-nuclei), total cp-DNA content,number of cp-nuclei, oxygen-evolution activity and chlorophyll (a and b) content wereexamined during the degeneration and development of chloroplasts, usin Chlamydomonasgreinhardii cells which had been incubated on solid medium for various periods.Under 4'-6-diamidino-2-phenylindole (DAPI) epifluorescence microscopy, eachcell that had been incubated for 7 days had one cell nucleus, one cup-shaped chloroplastand abou 1t 0 small, dispersed cp-nuclei in the chloroplast. One day after incubationof these cells on fresh medium, the cell volume and cp-nuclei increased in size 2-3 fold,but rapidly decreased in size after cell division. Afte 7 days orf abou incubationt , cellsceased to divide and cp-nuclei began to associate with each other. At about 20 daysthey formed a ring-shaped structure surrounding the pyrenoid, followed by condensationinto one cp-nuclear particle near the pyrenoid. When 41-day-old cells, having only onecp-nucleus, were reinoculated on fresh solid medium, the cp-nucleus increased in size2-3 fold, divided into several cp-nuclear particles and then dispersed into the chloroplast,forming a bead-like structure, before cell division. From microscopic fluorometry,a 4-fold increase in total cp-DNA content per chloroplast, without an increase in thenumber of cp-nuclear particles per chloroplast, occurred one day after the start of theexperiment and one day after reinoculation of 41-day-old cells onto fresh medium. Theprocess of condensation of dispersed cp-nuclear particles into one cp-nucleus duringdegeneration of the chloroplast was not accompanied by any change in total cp-DNAcontent per chloroplast. A large peak of oxygen-evolution (0.6-0.9 pmoles/cell/hour)was seen one day after inoculation and reinoculation of the cells. The chlorophyllcontent (a+b) was high (1.2-2.2 pg/cell) during the first week of incubation, after whichit gradually decreased.Key words: Chlamydomonas — Chloroplast degeneration — Chloroplast development— Cp-DNA — Cp-nucleus — Oxygen evolution.