Diurnal Regulation of Leaf Photosynthesis Is Related to Leaf-Age-Dependent Changes in Assimilate Accumulation in Camellia oleifera

Abstract

In order to clarify the mechanism of diurnal changes in photosynthesis of leaves of different leaf ages in Camellia oleifera, current-year leaves (CLs) and annual leaves (ALs) were used as the test materials to analyze the diurnal changes in photosynthetic parameters, assimilate contents and enzyme activities, as well as structural differences and expression levels of sugar transport regulating genes. The rate of net photosynthesis in CLs and ALs was highest in the morning. During the day, there was a decrease in the CO2 assimilation rate, and this decrease was greater in ALs than in CLs at midday. The maximal efficiency of photosystem II (PSII) photochemistry (Fv/Fm) showed a decreasing trend as the sunlight intensity increased, but no significant difference between CLs and ALs was found. Compared with CLs, ALs showed a greater decrease in the carbon export rate at midday and the levels of sugars and starch increased significantly in ALs, accompanied by higher enzyme activity of sucrose synthetase and ADP-glucose pyrophosphorylase. In addition, compared with CLs, ALs had a larger leaf vein area and higher leaf vein density, as well as higher expression levels of sugar transport regulating genes during the day. It is concluded that the excessive accumulation of assimilate is an important factor contributing to the midday depression of photosynthesis in Camellia oleifera annual leaves on a sunny day. Sugar transporters may play an important regulatory role in excessive accumulation of assimilate in leaves.

Sugar Receding in Aril Benefits the Recalcitrant Seeds of Litchi (Litchi chinensis) and Longan (Dimocarpus longan) to Cope with Dry Spells after Maturation

“…The supernatants of the two extractions were combined and 200 µL of the combined extract was added to 1.3 mL of the anthrone-sulfuric acid reagents from the Micro Plant Soluble Sugar Content Assay Kit (Solarbio, Beijing, China) and heated in a 95 • C water bath for 10 min. After cooling to room temperature, the absorbance of the reaction solution was determined at 620 nm according to the method by Zhang et al [33] by using a microplate spectrophotometer (51119670DP/Multiskan Sky with Touch Screen, Thermo Scientific, Waltham, MA, USA). Various concentrations of glucose solutions (0.00625-0.2 mg/mL) were used to construct a standard curve and the soluble sugar contents in the extracts were calculated based on the standard curve.…”

“…The content of the sugar moieties after hydrolyzation was determined using the anthrone-sulfuric acid colorimetry method as described in Section 2.8. The starch content in the residue was calculated with a Micro Plant Starch Content Assay Kit (Solarbio, Beijing, China) according to the method by Zhang et al [33]. The data were collected from five biological replicates.…”