Bench-grafted 'Fuji/M.26' apple (Malus domestica Borkh.) trees received a constant nitrogen (N) supply (10.7mM) from bud break to the end of June, and were then fertigated with 0, 5, 10, 15 or 20mM N in a modified Hoagland's solution for 2 months during the summer. In mid-October, half of the trees fertigated at each N concentration were sprayed twice with 3% urea, whereas the remaining trees served as controls. All trees were harvested after natural leaf fall and were stored at 2℃. Five trees from each of the N treatment combinations were destructively sampled during dormancy to determine the composition of N and total nonstructural carbohydrates (TNC). As the N supply from fertigation increased, amounts of N in both free amino acids and proteins increased, whereas C/N ratios decreased. Foliar urea applications in the fall significantly increased amounts of N in both free amino acids and proteins, but decreased their C/N ratios. Arginine, the most abundant amino acid in both free amino acids and in proteins, accounted for an increasing proportion of N in free amino acids and proteins with increasingNsupply from fertigation or foliar urea application. The ratio of proteinNto free amino acidNdecreased from about 27.1 to 3.2 as N supply from fertigation increased from 0 to 20mM, and decreased further to 3.0 in response to foliar urea applications in the fall. Concentrations of glucose, fructose, sucrose and TNC decreased as theNsupply from fertigation increased, whereas concentrations of sorbitol and starch remained relatively unchanged. Foliar urea applications decreased the concentration of eachTNCcomponent and theTNCconcentration in each N fertigation treatment. A negative linear relationship was found between carbon in TNC and N in proteins and free amino acids. The sum of carbon in TNC, proteins and free amino acids remained constant in response to N supply from fertigation. However, foliar urea applications decreased the sum of carbon in proteins, free amino acids and TNC because about 21% of the decrease in TNC carbonwas not recovered in free amino acids or proteins.Young apple trees storeNand carbon dynamically in response to N supply. As N supply increases, an increasing proportion of N is found in the form of free amino acids, which have a low carbon cost, although proteins remain the main form of N storage. Furthermore, part of the carbon from TNC is incorporated into amino acids and proteins, proteins, decreasing the carbon stored as TNC and increasing the carbon stored as amino acids and proteins.

通过对原产于不同地区的51个杏品种的性器官发育和结实性的系统调查和测定，结果表明，1. 花粉大小和形状少数虽有一定差异，而绝大多数品种相似，品种问花粉萌发率尽管差异很大，但所有品种均为花粉可育型；2. 大多数品种不完全花百分率很高，自然授粉结实率很低，其主要原因是雌蕊败育；3. 品种间不完全花百分率与花粉萌发率呈正相关；4. 欧洲生态群品种与中国生态群品种比较花粉大小和形状基本相似，而花粉萌发率和不完全花百分率低，自然授粉结实率高；5. 欧洲生态群品种能白花结实，而中国生态群品种均为自花不实品种。

The objective of this study was to determine how xanthophyll cycle-dependent thermal dissipation and the antioxidant system in the peel of apple fruit respond to the natural light exposure within the tree canopy. Fruit from exterior and interior canopies of both mature 'Gala' and 'Smoothee' apple trees were sampled at noon and/or predawn to measure chlorophyll fluorescence, xanthophyll cycle pool size and composition, and enzymatic and non-enzymatic antioxidants. Compared with the shaded side, the sun-exposed peel of the fruit had more excess absorbed photon flux density (PFD) as a result of a lower photosystem II operating efficiency and a higher incident PFD at noon. The efficiency of excitation transfer was lower in the sun-exposed peel than in the shaded peel, indicative of higher thermal dissipation. The sun-exposed peel had a larger xanthophyll cycle pool size and a higher conversion state. It also had higher activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, and a larger size and a higher reduction state of the ascorbate pool and the glutathione pool. However, catalase activity was lower in the sun-exposed peel than in the shaded peel. Superoxide dismutase did not show significant trend with regard to fruit peel type or position in the canopy. We conclude that both the xanthophyll cycle and the ascorbate/glutathione pathway in the apple fruit peel are acclimated to the prevailing light exposure within the tree canopy to meet the respective needs for dissipating excess absorbed PFD and detoxifying reactive oxygen species.

Libertyʼ) were monitored in the fi eld over a diurnal course at about 3 months after full bloom. Compared with leaves, sun-exposed peel of apple fruit had much lower photosystem II operating effi ciency at any given photon fl ux density (PFD) and a larger xanthophyll cycle pool size on a chlorophyll basis. Zeaxanthin (Z) level increased with rising PFD in the morning, reached the highest level during midday, and then decreased with falling PFD for the rest of the day. At noon, Z accounted for >90% of the xanthophyll cycle pool in the fruit peel compared with only 53% in leaves. Effi ciency of excitation transfer to PSII reaction centers (Fv'/Fm') was negatively related to the level of Z in fruit peel and leaves throughout the day. In fruit peel, the antioxidant enzymes in the ascorbate-glutathione cycle, ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) showed a diurnal pattern similar to that of incident PFD. In contrast, the activities of APX and GR in leaves did not change signifi cantly during the day although activities of both MDAR and DHAR were higher in the afternoon than in the morning. In both fruit peel and leaves, superoxide dismutase activity did not change signifi cantly during the day; catalase activity showed a diurnal pattern opposite to that of PFD with much lower activity in fruit peel than in leaves. The total ascorbate pool was much smaller in fruit peel than in leaves on an area basis, but the ratio of reduced ascorbate to oxidized ascorbate reached a maximum in the early afternoon in both fruit peel and leaves. The total glutathione pool, reduced glutathione and the ratio of reduced glutathione to oxidized glutathione in both fruit peel and leaves also peaked in the early afternoon. We conclude that the antioxidant system as well as the xanthophyll cycle responds to changing PFD over the course of a day to protect fruit peel from photooxidative damage.