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Dongmei Wei, Huimin Xu and Ruili Li

Anthers contain starch and neutral lipids, which have key roles in microspore ontogeny and gametophyte development. In this study, we observed the dynamic changes in starch and neutral lipids in the anther developmental processes of castor (Ricinus communis) by cytochemical methods. Starch grains and neutral lipids presented a regular dynamic distribution during anther development. In young anthers, some neutral lipids accumulated in sporogenous cells, whereas neutral lipids disappeared with microspore growth. At the late microspore stage, starch grains began to accumulate in microspores, and the starch content of bicellular pollen significantly increased after microspore mitosis. At anthesis, starch grains and neutral lipids accumulated in the mature pollen grains. Visible changes occurred in anther wall cells. The epidermis, middle layer, and tapetum were degenerated, and only a single layer of endothecium remained at anthesis. The dynamic variation of starch grains and neutral lipids in tapetal cells was consistent with the changes in microspores and pollen during anther development. All these findings demonstrated that tapetal cells directly interacted with the developing gametophytes. The tapetal cells play an important role in supplying nutritional substances for microspore absorption. Moreover, the endothecium protects the pollen and contributes to anther dehiscence. The results of this study provide a foundation for the further research on sexual reproduction in angiosperms.

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Huiling Wang, Wei Wang, Weidong Huang and Haiying Xu

Salicylic acid (SA) as a plant signal molecule plays an important regulatory role in stimulating the accumulation of plants’ defensive compounds. Numerous studies have shown its regulating effects on the biosynthesis of flavonoids. However, the controlling mechanism needs to be made clear further. Here, Vitis vinifera L. ‘Cabernet Sauvignon’ cell suspension cultures were treated with SA and its synthesis inhibitor paclobutrazol (Pac) to investigate their effects on flavonoid biosynthesis. The accumulation of gene transcripts and proteins of flavonoid biosynthesis pathway enzymes, including chalcone synthase (VvCHS), chalcone isomerase (VvCHI), dihydroflavonol 4-reductase (VvDFR), and anthocyanidin synthase (VvANS), were detected using real-time polymerase chain reaction (RT-PCR), quantitative polymerase chain reaction (qPCR), and western-blotting techniques. The results showed that treatment with exogenous SA at the proper concentration enhanced the production of flavonoids such as anthocyanins and proanthocyanidins (PAs) inside the suspension-cultured cells. The induction of anthocyanins and PAs was found to be time course-dependent. The mRNA and protein accumulation of VvCHS, VvCHI, VvDFR, and VvANS in the treatment system were enhanced too, and the changes were observed concomitantly. Treatment of Pac inhibited the induction of the accumulation of gene transcripts and proteins in accordance with the decreased accumulation of flavonoids. These results suggest that exogenous SA could induce both transcript and protein accumulation of flavonoid biosynthesis-related enzymes and in turn enhance the accumulation of flavonoid compounds such as anthocyanins and PAs in suspension-cultured grape cells.

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Jinhong Yuan, Man Xu, Wei Duan, Peige Fan and Shaohua Li

The responses of photosynthesis, chlorophyll fluorescence, and de-epoxidation state of the xanthophyll cycle pigments (DEPS) of micropropagated apple trees (Malus ×domestica) were investigated under whole-root water stress (WRS) and half-root water stress (HRS) induced by polyethylene glycol 6000 to simulate whole and partial root zone drying. Compared with control plants without water stress, plants under WRS and HRS exhibited reduced leaf net photosynthetic rate (Pn) and stomatal conductance (g S) with a greater reduction in WRS than in HRS plants. However, intercellular CO2 concentration (Ci) increased under WRS as water stress was prolonged, signifying a non-stomatal limitation of Pn. Regarding HRS, decreased Pn was mainly the result of a stomatal limitation explained by a relatively low Ci. Changes in photosynthesis and chlorophyll parameters indicate that severe and slight damage occurred to the photosynthetic apparatus of WRS and HRS leaves, respectively, starting at Day 3 after initiating water stress. This damage was not evident on the donor side but was expressed as a reduced capacity of the acceptor side of the photosystem II reaction centers. To prevent damage from excess light, the DEPS of WRS leaf increased. Decreased g S could explain reduced water use under an irrigation strategy of partial root zone drying in fruit trees.

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Wei Zheng, Xiao-Dan Xu and Long-Qing Chen

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Wei Zheng, Xiao-dan Xu, Kai-Ge Zhao and Longqing Chen

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Dawei Shi, Xiaodong Wei, Guoxiang Chen and Yanli Xu

Ginkgo (Ginkgo biloba), a dioecious tree species, is widely distributed throughout the world, yet little is known about sex-related responses to autumnal senescence in ginkgo. The aim of this study was to investigate changes in photosynthetic activities, concentration of oxidative stress parameters [malondialdehyde (MDA) and H2O2] and antioxidant systems, and ultrastructure of chloroplasts in the naturally senescing leaves of two ginkgo sexes and to examine whether progression of senescence is sex-specific in ginkgo. Photosynthesis in ginkgo leaves of both sexes was not limited by stomatal factors, but rather non-stomatal factors such as decreased photosynthetic pigments and photochemical activities that became more important during autumnal senescence. The responses of antioxidative enzymes were different from those of antioxidants to leaf senescence. Correlation analysis revealed that autumnal leaf senescence was significantly correlated to antioxidative enzymes changes but not to antioxidants such as ascorbate (ASA) and glutathione (GSH). Guaiacol peroxidase (POD) became more important in senescing leaves and played a major protective role, especially at the late stage of senescence. The shape of chloroplasts of both sexes changed from oblong to round, and there was an increase in the number and size of osmiophilic granules during senescence; swollen thylakoid membranes in the stroma and grana with a significant increase in MDA content were also observed. During autumnal senescence, female ginkgo plants showed smaller decreases in net photosynthetic rates, photosynthetic pigments, photochemical activities, superoxide dismutase, ascorbate peroxidase and catalase activities, higher POD activity, ASA and GSH contents, and smaller increases in H2O2 and MDA contents than did males. In addition, female plants had a later senescence of chloroplasts, a smaller accumulation of osmiophilic granules, and a slower rate of membrane damage. These results show that female ginkgo exhibit slower leaf senescence, which may be related to increased reproductive costs.

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Xiaojuan Zong, Jiawei Wang, Li Xu, Hairong Wei, Xin Chen, Dongzi Zhu, Yue Tan and Qingzhong Liu

Improving the poor resistance to environmental stress and the weak development of roots system in the cherry (Prunus) rootstock ‘Gisela 6’ (Prunus cerasus × Prunus canescens) is of great importance for sustainable sweet cherry (Prunus avium) production. Although a stable genetic transformation system has been developed for ‘Gisela 6’ rootstock, there is little information on the identification of genes involved in stress resistance. Using the cherry rootstock cultivar Gisela 6, we identified a total of 12 novel mitogen-activated protein kinase (MAPK) genes, designated PcMPKs. Phylogenetic analysis revealed that the PcMPKs could be divided into four groups, designated A, B, C, and D. In addition, an intron–exon structure analysis for the PcMPKs was conducted to help further understand the structure–function relationships within the cherry family. The expression profiles of PcMPKs in response to abiotic and biotic stresses were characterized using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Five PcMPKs (i.e., PcMPK4-1, PcMPK4-2, PcMPK3, PcMPK6, and PcMPK18) exhibited differential expression, and suggested their potential roles in plant responding to various stresses. This study provides the basis for further analysis on the physiological functions of PcMPKs in environmental tolerance in cherry rootstocks.

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Zhiyong Hu, Min Zhang, Qigen Wen, Jie Wei, Hualin Yi, Xiuxin Deng and Xianghua Xu

Seedlessness is of commercial importance in citrus (Citrus L.). Seedless ‘Ougan’ mandarin (C. suavissima) was selected from a bud sport mutation that occurred in ‘Ougan’ mandarin. We analyzed their pollen viability through KI-I2 and FDA staining, and examined the anthers of wild-type (seedy) and seedless mutant ‘Ougan’ mandarin using histological and cytochemical methods to characterize the process of pollen development. No pollen fertility was detected in this mutant. Pollen abortion in anthers of the mutant occurred at the tetrad stage of microspore development, and almost all the tetrads were abnormal. The mutant had heterogeneous microspore populations, including monads, dyads, triads, tetrads, and polyads in the same microsporangium. Pollen grain number per anther of the mutant was 21.9% less than the wild type. Morphology of mature pollen grains using SEM showed that the shape of mature pollen grains from both wild type and mutant is similar, but the microsporangia of the latter contained pollen grains of more variable sizes. At the early mature pollen grain stage, abundant starch grains and lipids appeared in the wild type's pollen, but fewer amounts were observed in the mutant. Moreover, the tapetal cells of the wild type accumulated lipids, but not those of the mutant. Results indicated that the abnormal development of the microspore led to pollen abortion in the mutant, and this could be the reason for its seedlessness. However, the genetic reasons for the aberrant tetrads are not clear and are under investigation.

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Mingxiu Liu, Peng Wang, Xu Wei, Qing Liu, Xiaolin Li, Guolu Liang and Qigao Guo

Triploid loquat (2n = 3x = 51) has stronger growth vigor and larger leaves, flowers, and fruit compared with its diploid parental plant (2n = 2x = 34), but the effects of triploidization on the contents of flavonoids and phenolics in leaves and flowers, which are the most important antioxidant compounds for pharmacological applications, have not been reported. In this report, 58 triploid loquat genotypes and seven corresponding diploid parental cultivars were used to evaluate the effects of triploidization on the contents of total flavonoids and phenolics and the antioxidant activities of leaves and flower buds. The results showed that the contents of total flavonoids and phenolics and their corresponding antioxidant activities were higher in most of the triploid loquat genotypes than their diploid parents. The antioxidant activities of leaves and flower buds were significantly correlated with the total flavonoids and phenolics contents in both diploid loquat and triploid loquat. It could be inferred that triploidization could increase the contents of flavonoids and phenolics in leaves and flower buds of loquat. Notably, the contents of total flavonoids and phenolics of leaves in triploid genotype ‘H3/24’ were the highest, reaching 212.00 mg rutin equivalent (RE)/g DW and 93.06 mg gallic acid equivalents (GAE)/g DW, respectively, which were significantly higher than those previously reported. Such a valuable trait may be stacked with other triploid traits that are already established, such as larger vegetative organs and better tolerance to various stresses, as a feasible strategy for breeding loquat cultivars with high pharmaceutical potency.

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Chun-Yan Han, Gui-Fen Luo, Li Ji, Wei-Bang Sun, Xu-Yang Fu and Cong-Ren Li