Changes in the Ability of Photophosphorylation and Activities of Surface‐Bound Adenosine Triphosphatase and Ribulose Diphosphate Carboxylase of Chloroplasts Isolated from the Barley Leaves Senescing in Darkness

Abstract

Dark induced aging of detached primary leaves of 11-day-old barley seedlings brings about a significant decline in the rates of ferricyanide |Fe(CN)jJ'" reduction and photophosphorylations of isolated chloroplasts. Ferricyanide-supported noncyclic photophosphorylation is somewhat more susceptible to leaf aging than phenazine methosulfate (PMS)-supported cyclic phosphorylation. Non-latent membrane-bound adenosine triphosphatase (ATPase) and ribulosediphosphate carboxylase (RuDPCase) lose about half of their initial activities after 24 h, while during this period the electron transport and photophosphorylation activities are much less affected. Also, the loss of RuDPCase is almost complete, while chloroplasts still exhibit a significant level of iFe(CN)^]'" reduction and photophosphorylations after 7 days of dark incubation. This would suggest that the enzymatic dark reactions are more sensitive to aging stress than the primary photochemical reactions of chloroplasts.Studies on the effect of divalent cations such as Mg^+ and Ca^+ on non-latent ATPase activity revealed that the dark stressed aging of detached leaves brings about a time dependent alteration in the response of this enzyme to Mg-'^, but not to Ca^+. The former showed inhibitory as well as stimulatory response, whereas the latter always caused the usual stimulation. Addition of kinetin (50 M) ensured retention of |Fe(CN)J^-reduction, photophosphorylations and RuDPCase activity in chloroplasts during leaf aging, but it failed to preserve the initial loss in the activity of the non-activated membrane-bound ATPase.

Chlorophyll Content, Hill Reaction and PEPcase Activity in Relation to Hybrid Vigour in Pearl Millet during Early Seedling Growth

“…Hill activity was estimated in chloroplasts isolated according to BiSWAL and MOHANTY (1978) with some modifications. The isolation medium consisted of 0.05 M Na-phosphate buffer (pH 7.8), 0.01 M EDTA, 0.01 M NaCl and 0.4 M sucrose.…”

Photosynthetic analysis of mid-vein and leaf lamina in high-yield hybrid rice in fields during senescence

“…For example, lower thermoluminescence values (indicative of damage to PSII) were recorded in Arabidopsis thaliana during senescence (Wang et al2016). Speci cally, activities of the whole electron transport chain and reaction center decline acutely at the onset of senescence (Biswal and Prasanna 1978;Prakash et al 1998). This is coincident with a loss in redox homeostasis in the electron transport chain between PSI and PSII, caused by an increase in the quantity of reduced quinones, representing an energy imbalance.…”

Ageing of chloroplasts in vitro ? III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

“…Extensive studies have been made on the degradation of chloroplasts in vivo during leaf senescence which causes a loss in photoelectron transport [2,8,9,17], photophosphorylation [5,16] and CO2 fixation [5,16]. Leaf senescence also results in alterations in the absorption and fluorescence properties of photosynthetic pigments [3,6,19].…”