The age dependence of the photosynthetic performance, chlorophyll fluorescence and chloroplast ultrastructure of green form and Chl ft-deficient form (aurea) of tobacco Su/su mutant were compared. The most pronounced differences between the aurea and green tobacco found in young leaves diminished with leaf age. Slower accumulation of the photosynthetic pigments during the development of aurea leaves was accompanied by a slower accumulation of LHC antennae of both photosystems, particularly that of PS2, and by retention of an increase in the capacity of PS2 photochemistry, measured as Fy/FM The ratio Fv/Fm, however, increased rapidly during maturation of aurea leaves, and fmally the mature aurea leaves exhibited higher values of this ratio than the green ones. Rates of photosynthesis at saturating irradiance (Epiax) saturating CO2 concentration (/’sat) decreased with leaf age for both aurea and green tobacco, being always higher in aurea leaves than in leaves of green tobacco of comparable age. AU these characteristics indicated retarded development of aurea leaves. Also the chloroplast ultrastructure, particularly grana formation, exhibited slower development. The decrease in /Wx and with leaf age in both tobacco forms and retardation in the development of aurea leaves can explain higher value of usually found in aurea tobacco.
Postconditioning (PostC) is a re cently discovered phenomenon whereby brief repetitive cycles of ischaemia with intermittent reperfusion following prolonged is chaemia elicit cardioprotection. This study investigated whether the age, genetic characteristics or number of repetitive cycles influenced the protective effect of PostC in mice. C57BL/6 floxed or non-floxed STAT-3 mice aged between 14-16 weeks (young) or 18-20 weeks (older) were perfused on a Langendorff apparatus and subjected to 35 min global ischaemia and 45 min reperfusion. PostC was elicited by either 3 (PostC-3) or 6 cycles (PostC-6) of 10s ischaemia and 10 s reperfusion. PostC-3 and PostC-6 in both young and older non-floxed mice reduced the myocar dial infarct size. In contrast, only PostC-3 reduced myocardial infarct size in young floxed mice. Neither PostC-3 nor PostC-6 reduced the in farct in older floxed mice. Our data reveal that genetic characteristics, a minute difference in age or the nu mber of postconditioning cycles are critical factors to be consid ered for the successful effect of ischaemic postconditioning in a murine model. Moreover, these factors should be taken into consideration for future experimental research or clinical applications of this protective phenomenon., S. J. Somers ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
Age-associated changes in large blood vessels were characterized by increased arterial wall thickness, luminal dilation and impaired endothelial function. But little is known about the effect of age on structural and functional changes in small resistance arteries. The mechanisms underlying age-associated endothelial dysfunction in rat mesenteric resistance arteries were investigated in the present study. Small rat mesenteric arteries were excised and cannulated, and vascular endothelial functions were tested by acetylcholine (ACh). Our experiments showed (1) endotheliumdependent vasorelaxation induced by ACh was reduced in aged mesenteric arteries; (2) blockade of Kca channels markedly reduced the vasodilation in young and adult rats, the resultant reduction in aged rats was much smaller compared with young and adult rats; (3) inhibition of endothelial nitric oxide synthase (NOS) resulted in a significant reduction of vasodilation in young and adult, but there was a smaller reduction in aged rats. The results suggest that (1) endothelial function was impaired in mesenteric arteries of aged rats; (2) both Kca channels and nitric oxide (NO) contribute together to the ACh-induced vasorelaxation in small mesenteric arteries, and (3) both the impairment of Kca channel function and decreased NO account for the age-related endothelial dysfunction., E. Zhou, D. Qing, J. Li., and Obsahuje bibliografii a bibliografické odkazy