Effect of Light Quality on Photosynthesis and Chlorophyll Fluorescence in Strawberry Leaves

The photosynthetic characteristics of strawberry (Fragariaananassa Duch. cv. Toyonoka)leaves under illumination of identical light intensity(55-57% natural light) withdifferent light quality were studied. It was showed that the chlorophyll content,maximal photochemical efficiency of PSⅡ(Fv/Fm), Fm/Fo, amount of inactive PSⅡreactioncenters (Fi-Fo) and rate of QA reduction were positively correlated with the red-light/blue-light ratios, but the chlorophyll (a/b) ratios were negatively correlated withthem. Carotenoid content of the leaves was maximum under the blue film, than under greenfilm, red film, white film and yellow film, and negatively correlated with the red/far-red ratios. The apparent quantum yield (AQY), photorespiratory rate (Pr) and carboxylationefficiency (CE) were also strongly affected by light quality. The photosynthetic rate(Pn) in strawberry leaves under green film was significantly lower than under all otherfilm. Our results suggested that light quality is an essential factor regulating thedevelopment of PSⅡ, and phytochrome and an independent blue light photoreceptor,possibly a cryptochrome, can regulate photosynthetic performance.

Analysis of Major Carotenoid Composition and Its Content of Citrus Fruit

α-carotene, β-carotene, lycopene, β-cryptoxanthin, zeaxanthin and lutein content of fruits in 53 citrus cultivars were determined using HPLC. In both peel and pulp of citrus fruit, the major carotenoids were lutein, zeaxanthin and β-cryptoxanthin. β-carotene content was relatively low and extremely low was the amount of α-carotene. Among the 53 cultivars tested, lycopene was detected only in pulp of Cara Cara navel orange. Carotenoid content in both peel and pulp of citrus fruit was the highest in Citrus reticulata Blanco and lowest in Citrus grandis Osbeck. Consequently, as far as the health protection value is considered, fruit of Citrus reticulata Blanco ranks probably higher than other citrus fruits. In fruit of most Citrus reticulata varities, β-cryptoxanthin was the main carotenoid component in pulp and its amount approximated that of lutein in peel. Content of lutein, zeaxanthin and β-cryptoxanthin in peel was about 2.515 times that in pulp on the basis of fresh weight. Thus peel was inferred to be the principal location for the carotenoid stock in citrus fruit.

The Physiological Mechanism of Postphloem Sugar Transport in Citrus Fruit

The dynamics of translocation and partitioning of 14C-phothsynthates, the concentration of sucrose in fruit tissues and the effects of the membrane carrier- and ATPase-specific inhibitors on 14C-sucrose uptake by juice sacs of the satsuma mandarin(Citrus unshiu Marc. cv. Miyagawa wase)fruit were examined at the stage of fruit enlargement and fruit full ripe. Kinetic data of 14C-photosynthate translocation indicated that the rate of photosynthate transport into juice sacs decreased with fruit maturation and sugar accumulation. Along the photosynthate translocation path, i. e. from vascular bundles to segment epidermis then to juice sacs, a descending sugar gradient was observed. With fruit maturation and sugar accumulation in juice sacs, the 14C photosynthate gradient increased, whereas the static sucrose concentration gradient decreased with fruit maturation and sugar accumulation. The higher gradient of specific 14C radioactivity was considered to favor diffusion and sugar transport into juice sacs at the later stage of fruit development. The rate of uptake 14C-sucrose by juice sacs of satsuma mandarin fruit was markedly reduced by PCMBS, EB, DNP and NO3-treatment. The above results suggested the participation of a carrier-mediated, energy-dependent sugar active transport process in juice sacs of satsuma mandarin fruit.

Physiological Mechanism on the Difference of Sugar Accumulation in Four Citrus Varieties

The concentration of sucrose, glucose, fructose, titratable acid, ABA and the activity of acid invertase (AI) were measured in juice sacs of Bendizao mandarin (Citrus succosa Hort), Ponkan (Citrus reticulata Blanco), Miyagawa wase (Citrus unshiu Marc) and Meyer lemon (Citrus meyeri Y). The acid hydrolysis of sucrose in vitro was also studied. The results showed that the sugar content, the ratio of different sugars, titratable acidity, ABA content and the activity of AI were obviously different in four citrus varieties. The sugar content in juice sacs of citrus fruit was related to that of ABA at the late stage of fruit development. The result suggested that ABA played an important role in sugar accumulation in juice sacs of citrus fruit. Bendizao mandarin and Miyagawa wase mainly accumulated sucrose in juice sacs of citrus fruit. Meyer lemon accumulated hexose, and Ponkan citrus was the sucrose-hexose accumulating type variety. In Meyer lemon with high acid degree, the composition of sugar in juice sacs was determined by acid-hydrolysis of sucrose. In Bendizao mandarin, Ponkan citrus and Miyagawa wase with low acid degree, the composition of sugars at the late stage of fruit development was obviously affected by the AI activity.