| The newly germinating leaf of red leaf peach is brilliant red in spring, but would turn green under the high tempreture condition in summer, as leaf age increasing, the basal leaves gradually turn from dark red to green, anthocyanin content decrease. In contrast, many early maturing peach varieties have dark green leaves before fruit harvest, and anthocyanin accumulation starts in the leaf petiole, main vein and spread along the vein. Leaf color gradually turn to purple-red from the basal leaves to the top. Because of the speciality of its leaf coloring, the early maturing peach has important theoretical and practical significance to the development and application prospects in gardening, but also on enriching the research of color emerging mechanism and photosynthetic characteristics of colored-leaf plants.This research selected tow red leaf color peach cultivars (’tsuku-ba-5’,’Rutgers redleaf) and two early maturing peach cultivars (’Zaomei’’Chunlei’), which leaves turn red in summer, as the trail materials, green leaf peach cultivar ’Honghuabitao’ as CK, analyzed and compared their leaf pigments, soluble sugar and starch contents, anthocyanin biosynthesis related enzymes activity, photosynthesis and chlorophyll fluorescence characteristics in their growth season(June to October), studied physiological mechanism of leaf color change, the photosynthetic characteristics of peach with different coloration types, and the correlation between these indexes and environmental factors.1. Comparison of seasonal changes of leaf color and related physiological mechanism of peach with different coloration types.The variation of leaf anthocyanin content of red leaf peach showed a significant bimodal curve, and had one each peak respectively in early July and mid-september, and a apparent low point in mid-August, that caused obvious turning-green phenomenon in summer.The leaf soluble sugar and starch contents of red leaf peach had no significant differences with green leaf peach, and there was significant positive correlation between leaf anthocyanin content and total sugar content, CHI activity, but no markedly pertinence with environmental factors and PAL activity. The turning-green phenomenon of red leaf peach in summer, on the one hand, due to the rapid degradation of anthocyanin caused by the high temperature, but the main reason may be anthocyanin synthesis blocked caused by the lack of leaf CHI and DFR activity.The leaf anthocyanin of early maturing peach started synthesis and accumulate after fruit harvest in mid June. Ant/Chl reached at a stable level in mid August, for the high chlorophyll content, leaves showed dark purple at last. The leaf soluble sugars content of early-maturing peach had no significant differences with red leaf peach in spring and summer, but significantly lower than those in red leaf peach and green leaf peach in autumn. The leaf anthocyanin content and leaf color of early-maturing peach significantly positive correlated with PFD and CHI activity. There was significant positive correlation between DFR activity and leaf color, and DFR activity had the same trend with leaf anthocyanin content. The leaf anthocyanin content of green leaf peach kept a low level throughout the experiment period.2. Comparison of photosynthetic characteristics and chlorophyll fluorescence parameters of peaches with different coloration typesThe net photosynthetic accumulation and water use efficiency (WUE) of early maturing peach had no significant differences with green leaf peach. Owing to the apparnt quantum yield (AQY) and carboxylation efficiency (CE) were significantly lower than those of early maturing peach and green leaf peach, the photosynthetic ability of red leaf peach was lower either.The increase of temperature and photon flux density (PFD) results in reduction of the stomatal conductance (Gs), minimal fluorescence (Fa) and non-photochemical quenching coefficient (NPQ) values of early-maturing peach. But the PSII maximal photochemical efficiency (Fv/Fm), PSII actual photochemical efficiency (φPSII) and photochemical quenching coefficient (qP) of early-maturing peach maintained high level. So its photosynthetic apparatus maintain a high energy capture, conversion efficiency and electron transport rate in the spring and summer. The photosynthetic ability of red leaf peach was influenced greatly by leaf anthocyanin content. The Fv/Fm、φPSII ETR of red leaf peach decreased significantly, but the NPQ and Gs values increased under the conditions of high temperature and high in summer. The antenna pigment of early-maturing peach degraded and carboxylation efficiency decreased in autumn, and the gap among the three was decreasing. Net photosynthetic rate of early maturing peach decreased earlier in late summer may be caused by antenna pigment degradation and carboxylase activity decline related to leaf senescence.3. Related physiological mechanism of red leaf phenomena of early maturing peach in summerthe accumulation of leaf anthocyanins is the main reason for leaves of early-maturing peach turning red in summer. The anthocyanins of ’Zaomei’ increased most rapidly, and leaf color changed early. CHI and DFR activities increased at early July. The leaf anthocyanins content and CHI activity of’Chunlei’both increased later than’Zaomei’. The DFR activity of early-maturing peach significantly higher than green leaf control, and was positively correlated with leaf anthocyanins content. Leaf anthocyanin content of early-maturing peach significantly positive correlated with leaf soluble sugar content at the former period of leaf coloring, and with PAL, CHI activities after leaf changed to be red. The soluble sugar and starch content of early-maturing peach and red leaf peach were lower than control during the experiment period. Therefore, leaf sugar content may be not the key factor of early-maturing peach leaf color changing.4. Effect of red leaf phenomena on photosynthetic characteristics of early-maturing peach in summerAnalylisis of leaf pigment content, net photosynthetic rate (Pn), PSII maximal photochemical efficiency (Fv/Fm), PSII actual photochemical efficiency (φPSII), electron transport rate (ETR), and the relative photosynthetic limitation(L(PFD)) showed that, early-maturing peach had great changes in photosynthetic and chlorophyll fluorescence characteristics despite the strong differences in leaf pigment composition. Pn, Fv/Fm and φPSII values of early-maturing peach increased, and no significantly photosynthetic inhibition was observed during the experiment. While’Honghuabitao’showed obvious photo inhibition in July, and ETR, Fv/Fm,φPSII values decreased.’Zaomei’, which was more intensity colored, had minor L(PFD). And it was more adaptive to high temperature and strong light in summer than’Chunlei’ and ’Honghuabitao’. Chlorophyll fluorescence quenching analysis indicate that leaf anthocyanin accumulation lead to a transitory increase of relative share of photochemical reaction (P) and heat dissipation (D) from antenna pigment absorbed light. The redden leaves had higher photochemical quenching coefficient (qP) than green leaves, and more effective PSII photochemical reactions. However the lower non-photochemical quenching coefficient (NPQ) values shown by redden leaves probably indicate a lower ability to dissipate excess photon energy safely than green leaves. |
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