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Zhou Li, Yan Peng and Bingru Huang

Gama-aminobutyric acid (GABA) is a nonprotein amino acid in plant cells, which responds to changes in environmental factors. The objectives of this study were to evaluate the effects of foliar spray of GABA on drought and heat tolerance in creeping bentgrass (Agrostis stolonifera), and to investigate physiological factors altered by GABA application that contribute to improved drought tolerance and heat tolerance. GABA-treated plants (cv. Penncross) or non-GABA-treated control plants were then subjected to the following three treatments in growth chambers: 1) nonstress control [plants irrigated every 2 days to maintain soil water content at the pot capacity and maintained at 21/19 °C (day/night) for 35 days], 2) heat stress [plants exposed to 35/30 °C (day/night) and well-watered conditions for 35 days], and 3) drought stress [plants unirrigated for 9 days and maintained at 21/19 °C (day/night), and then rewatered for 2 days]. As compared with untreated plants, GABA-treated plants showed 22% to 39% and 8% to 21% significantly lower leaf electrolyte leakage (EL) and 35% to 143% and 21% to 24% significantly higher turf quality (TQ), 8% to 17% and 17% to 24% relative water content (RWC), 22% to 39% and 25% to 27% chlorophyll content, 7% to 11% and 6% to 17% photochemical efficiency, and an 84% to 683% and 57% to 76% osmotic adjustment (OA) exposed to heat or drought stress across days of treatment, respectively. GABA-treated plants accumulated 7% to 10% more water-soluble carbohydrates (WSC) and 11% to 43% more free proline than nontreated plants under heat stress, and 12% to 30% higher accumulation of WSC under drought stress. After 2 days of rewatering, a significantly better recovery also was observed in GABA-treated plants than that in nontreated plants previously exposed to drought stress. The results suggest that foliar application of GABA significantly improved heat and drought tolerance of creeping bentgrass, which was associated with maintenance of cell membrane stability, delaying in leaf senescence, and enhancing OA. The effectiveness of exogenous GABA application was more pronounced under heat stress than under drought stress.

Open access

Zhou Li, Yan Peng and Bingru Huang

Small molecules, including H2O2 and Ca, mediate stress signaling and drought tolerance in plants. The objective of this study was to determine whether improvement in drought tolerance by H2O2 and Ca were associated with the regulation of transcription factors and stress-protective genes in perennial grass species. Plants of creeping bentgrass (Agrostis stolonifera) were sprayed with water (control), H2O2 (9 mm), or CaCl2 (10 mm) and exposed to drought stress for 20 days in controlled-environment growth chambers. Foliar application of H2O2 or Ca led to significant improvement in drought tolerance of creeping bentgrass, as demonstrated by greater turf quality, leaf relative water content, chlorophyll content, photochemical efficiency, and cell membrane stability, as compared with the untreated control. The application of H2O2 and Ca resulted in significant up-regulation of genes in Ca signaling transduction pathways [Ca-dependent kinase 26 (CDPK26), mitogen-activated protein kinase 1 (MAPK1), and 14-3-3] and transcript factors (WRKY75 and MYB13). For genes encoding antioxidant enzymes, H2O2 mainly enhanced superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and dehydroascorbate reductase (DHAR) expression, while Ca primarily improved transcript levels of SOD, monodehydroascorbate reductase (MDHAR), and GR. In addition, heat shock protein 70 (HSP70), metallothionein 1 (MT1), and glutamine synthetase 2 (GS2) were also markedly up-regulated by H2O2 and Ca under drought stress. However, the transcript level of lipoxygenase 3 (LOX3) was significantly down-regulated by H2O2 and Ca under well-watered and drought conditions. These results imply that H2O2 and Ca commonly or differentially regulate genes expression in association with drought tolerance through activating Ca signaling pathway and regulating transcription factors and stress-protective genes expression, leading to the alleviation of lipid peroxidation, maintenance of correct protein folding and translocation, and enhancement of nitrogen metabolism under a prolonged period of drought stress in creeping bentgrass.

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Shujuan Yang, Li Peng, Han Bao and Huiqiao Tian

Our goal was to determine the ultrastructure features and the dynamic changes in polysaccharides and neutral lipids in developing anthers of rose balsam (Impatiens balsamina), and to better understand the mechanisms controlling male reproductive development. Transmission electron microscope (TEM) techniques were used to study the ultrastructural characteristics of the anthers, and histochemical methods were used to determine levels of polysaccharides and lipids. The cytokinesis in the microsporocyte meiosis was simultaneous type, and microspore tetrads were mainly tetrahedral. The pollen exine began to form at the tetrad stage. The mature pollen grains were oval-shaped and bicellular. Accumulation of reserve substances began at the late microsporogenesis stage, and an abundance of starch grains and lipids were stored in pollen grains at anthesis. Polysaccharides and lipids changed in different stages and played an important role in anther development. Moreover, the calcium oxalate crystals may protect the pollen and suggest that calcium distribution is related to anther development.

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Fan Cao, Xinwang Wang, Zhuangzhuang Liu, Yongrong Li and Fangren Peng

Pecan cuttings are difficult for rooting. This study describes the pecan hardwood rooting process based on anatomic characteristics to understand root formation mechanisms of pecan cuttings. The expressed proteins of different periods during the adventitious rooting process of pecan seedling hardwood cuttings were identified and analyzed to evaluate the rooting mechanism. The expressed proteins of pecan cutting seedlings were also compared with other cultivar cuttings during the rooting period. Pecan seedling cuttings were developed at different air and substrate temperatures to induce root formation. Adventitious root formation of pecan hardwood cuttings was described, and the phloem at the base of the prepared cuttings was selected as the sample for the differential protein analysis. The results showed that adventitious root formation of pecan hardwood cuttings was the only product of callus differentiation, which originated from the cells of the cambium or vascular ray parenchyma. Such adventitious root primordia were developed from those calluses that formed the regenerative structure, and the expressed proteins during the adventitious rooting of pecan hardwood cutting were identified and analyzed by matrix-assisted laser desorption ionization–time of flight–mass spectrometry (MALDI-TOF-MS) to evaluate the rooting mechanism. Eight differentially expressed proteins were found in the rooting periods, and 15 differential proteins were found by comparing pecan cutting types, which were analyzed by peptide mass fingerprinting homology. The results show that the primordial cells were differentiated from the meristematic cells. Furthermore, the differentially expressed proteins contained energy metabolism proteins, adversity stress proteins, and signal transmission proteins. The energy metabolism-related proteins were adenosine triphosphate (ATP) synthase, photosynthesis-related proteins, and enolase. The adversity-stress proteins containing heat shock-related proteins and signal transmission proteins were mainly cytochrome enzymes and heme-binding proteins. Adventitious root formation of pecan cultivar hardwood cuttings was difficult. More trials should be performed from the potential aspects of high defensive protection and phloem morphologic structure.

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Fachun Guan, Shiping Wang, Rongqin Li, Mu Peng and Fanjuan Meng

To analyze the evolutionary level of Prunus mira Koehne (Prunus mira Koehne Kov et. Kpst), 15 kinds of pollen grains from five altitudes were observed using a scanning electron microscope (SEM). This study demonstrates that pollen morphous P. mira has high variation; specifically, individuals from higher altitudes are much more evolved than those from lower altitudes. This is the first time the pollen morphology of P. mira has been systematically illustrated. Furthermore, 12 random amplified polymorphic DNA (RAPD) primers generated clear and repeatable bands among all individuals based on RAPD; 107 bands ranging from 200 bp to 2000 bp were generated with an average of 8.92 bands per primer. Thus, the RAPD technique proved to be a powerful tool to reveal variation on P. mira. This study provides comprehensive information for genetic diversity of P. mira from different altitudes.

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Fan Cao, Yunchu Wei, Xinwang Wang, Yongrong Li and Fangren Peng

To describe the influence of different pecan seedling rootstocks on drought stress resistance, 12 rootstocks of ‘87MX1-2.2’, ‘87MX5-1.7’, ‘Elliott’, ‘Frutoso’, ‘Giles’, ‘Major’, ‘Moore’, ‘Peruque’, ‘Posey’, ‘Riverside’, ‘San Felipe’, and ‘VC1-68’ were selected as rootstock treatments for grafting. In addition, the experimental materials for the grafted young ‘Pawnee’ tree treatments included the pressure-volume technique (PV technique) and cutting shoot transpiration methods to plot the PV and the cutting shoot transpiration curves, and the parameters calculated from the two curves were used to analyze the data produced by the subordinate function and cluster dendrogram methods. The results revealed that the different seedling rootstock treatments influenced the ‘Pawnee’ grafted trees to varying degrees on aspects of drought resistance, the ability to save water, the modulation of osmosis, and the sensitivity of the stomatal response. The order of drought tolerance for these different pecan seedling rootstock treatments from high to low was as follows: ‘Posey’, ‘Peruque’, ‘Riverside’, ‘87MX5-1.7’, ‘VC1-68’, ‘Elliott’, ‘87MX1-2.2’, ‘San Felipe’, ‘Moore’, ‘Major’, ‘Giles’, and ‘Frutoso’.

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Tingting Zhao, Dawei Li, Lulu Li, Fei Han, Xiaoli Liu, Peng Zhang, Meiyan Chen and Caihong Zhong

Kiwifruit (Actinidia chinensis Planchon) is an economically important fruit, and its flowering and production are affected by the chill accumulation in winter. In this study, the chilling requirements of nine kiwifruit cultivars with three ploidy levels (diploid, tetraploid, and hexaploid) were analyzed by using the Dynamic Model, Utah Model, and chilling hours (CH) Model. The chilling requirements for vegetative budbreak of these kiwifruit cultivars were 24–55 chill portions (CP), 316–991 chill units (CU), and 222–853 CH, and the chilling requirements for floral emergence were 45–69 CP, 825–1336 CU, and 655–1138 CH. The chilling requirements for vegetative budbreak and floral emergence were significantly lower for diploid than hexaploid cultivars with tetraploid cultivars intermediate. Pearson correlation analysis indicated that ploidy levels were positively correlated with chilling requirement, with the cv of 0.74 and 0.82 for vegetative budbreak and floral emergence chilling requirements, respectively. In conclusion, these results provide some novel insights of kiwifruit varieties of various chilling requirements, which is beneficial for kiwifruit cultivar selection for different climates and environments.

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Shu’an Wang, Rutong Yang, Peng Wang, Qing Wang, Linfang Li, Ya Li and Zengfang Yin

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Xing-Zheng Fu, Fei Xing, Li Cao, Chang-Pin Chun, Li-Li Ling, Cai-Lun Jiang and Liang-Zhi Peng

To compare the effects of various zinc (Zn) foliar fertilizers on correcting citrus Zn deficiency and to explore an effective correcting method, three common Zn fertilizers, Zn sulfate heptahydrate (ZnSO4.7H2O), Zn chloride (ZnCl2), and Zn nitrate hexahydrate [Zn(NO3)2.6H2O], were selected to spray the Zn-deficient citrus leaves, tested at different concentrations, with or without organosilicone surfactant. Zn content, chlorophyll levels, and photosynthesis characteristics of leaves were analyzed. Leaf Zn content was significantly increased with increase of the sprayed Zn concentration of the three Zn fertilizers. However, when the sprayed Zn concentration of ZnSO4.7H2O exceeded 200 mg·L−1, and Zn concentration of ZnCl2 or Zn(NO3)2.6H2O exceeded 100 mg·L−1, obvious necrotic spots formed on leaves. This necrosis disappeared when 0.025% organosilicone was added to the three Zn fertilizer solutions, even at a Zn concentration of 250 mg·L−1. Meanwhile, the Zn contents of leaves increased one to four times for these treatments. Furthermore, foliar application of the three Zn fertilizers significantly improved chlorophyll levels and photosynthetic capacity of Zn-deficient leaves. The data of chlorophyll and photosynthesis characteristics indicate that the correcting effect of ZnCl2 and Zn(NO3)2.6H2O is better than that of ZnSO4.7H2O, and could be further improved via supplement of organosilicone. In conclusion, ZnCl2 or Zn(NO3)2.6H2O containing 250 mg·L−1 of Zn and supplemented with 0.025% organosilicone is a safe and effective formulation of Zn foliar fertilizer for correcting citrus Zn deficiency.

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Zhuang-Zhuang Liu, Tao Chen, Fang-Ren Peng, You-Wang Liang, Peng-Peng Tan, Zheng-Hai Mo, Fan Cao, Yang-Juan Shang, Rui Zhang and Yong-Rong Li

Cytosine methylation plays important roles in regulating gene expression and modulating agronomic traits. In this study, the fluorescence-labeled methylation-sensitive amplified polymorphism (F-MSAP) technique was used to study variation in cytosine methylation among seven pecan (Carya illinoinensis) cultivars at four developmental stages. In addition, phenotypic variations in the leaves of these seven cultivars were investigated. Using eight primer sets, 22,796 bands and 950 sites were detected in the pecan cultivars at four stages. Variation in cytosine methylation was observed among the pecan cultivars, with total methylation levels ranging from 51.18% to 56.58% and polymorphism rates of 82.29%, 81.73%, 78.64%, and 79.09% being recorded at the four stages. Sufficiently accompanying the polymorphism data, significant differences in phenotypic traits were also observed among the pecan cultivars, suggesting that cytosine methylation may be an important factor underlying phenotypic variation. Hypermethylation was the dominant type of methylation among the four types observed, and full methylation occurred at higher levels than did hemimethylation in the pecan genomes. Cluster analysis and principal coordinate analysis (PCoA) identified Dice coefficients ranging from 0.698 to 0.778, with an average coefficient of 0.735, and the variance contribution rates of the previous three principal coordinates were 19.6%, 19.0%, and 18.2%, respectively. Among the seven pecan cultivars, four groups were clearly classified based on a Dice coefficient of 0.75 and the previous three principal coordinates. Tracing dynamic changes in methylation status across stages revealed that methylation patterns changed at a larger proportion of CCGG sites from the 30% of final fruit-size (30%-FFS) stage to the 70%-FFS stage, with general decreases in the total methylation level, the rate of polymorphism, and specific sites being observed in each cultivar. These results demonstrated that the F-MSAP technique is a powerful tool for quantitatively detecting cytosine methylation in pecan genomes and provide a new perspective for studying many important life processes in pecan.