The decay of tyrosine cation radical was found to be biphasic at 253 K. The fast phase corresponds to the YZ* component while the slow phase corresponds to the tyrosine D radical (YD*) component. At 253 K, the t1/2 value was ∼28.6 s for the fast phase and ∼190.7 s for the slow phase. The fast phase is attributed to the recombination of charges between YZ* and QA-. The activation energy for the reaction of YZ with QA- between 253 and 293 K was 48 kJ mol-1 in Cl--depleted photosystem 2 (PS2) membranes. Both the decay rate and the amplitude of the PAR-induced signal of YZ* were affected by addition of chloride anion. Change in the decay rate and the amplitude of the PAR-induced signal of YZ* was observed when other anions like Br-, I-, F, HCO3-, NO3-, PO43- were substituted in the Cl--depleted PS2. and A. Jajoo, S. Bharti, A. Kawamori.
Field studies were conducted to investigate ontogenic changes in leaf photosynthesis and chloroplast ultrastructure of a single cotton (Gossypium hirsutum L.) leaf subtending the fruit. A 20-d old leaf was the most physiologically active with net photosynthetic rate (PN) of 16.5 μmol m-2 s-1 and nitrogen (N) concentration of 168 mmol m-2. These values declined with leaf age and a close relationship existed between them. Concurrent with declines in PN, ultrastructural alterations occurred in the chloroplast: the 20-d old leaf had increased grana number and thylakoids per granum and a few plastoglobuli. Afterwards, the grana number and thylakoids per granum declined with leaf age indicating disintegrated grana and stroma lamellae. Concomitant with disintegrated membrane system was the presence of numerous large plastoglobuli. The PN was closely related to grana number and thylakoids per granum suggesting that the decline in PN with leaf age was associated with ultrastructural changes in the chloroplast. and Bhaskar Rao Bondada, D. M. Oosterhuis.
In canopy shade leaves of grapevine (Vitis vinifera L. cv. Moscato giallo) grown in the field the contents of chlorophyll (Chl), carotenoids (Car), and soluble protein per fresh mass were lower than in sun leaves. RuBPC activity, in vivo nitrate reductase activity (indicator of nitrate utilisation), apparent electron transport rate, and photochemical fluorescence quenching were also significantly reduced in canopy shade leaves. When various photosynthetic activities were followed in isolated thylakoids, canopy shade leaves exerted a marked inhibition of whole chain and photosystem (PS) 2 activity. Smaller inhibition of PS1 activity was observed even in high-level canopy shade (HS) leaves. The artificial exogenous electron donors, DPC and NH2OH, significantly restored the loss of PS2 activity in HS leaves. Similar results were obtained when Fv/Fm was evaluated by Chl fluorescence measurements. The marked loss of PS2 activity in canopy shade leaves was due to the loss of 47, 43, 33, 28-25, 23, 17, and 10 kDa polypeptides. and M. Bertamini, N. Nedunchezhian.