The roles of abscisic acid (ABA) and nitric oxide (NO) and the relationship between NO and ABA on chilling resistance and activation of antioxidant activities in walnut (Juglans regia) shoots in vitro under chilling stress were investigated. Walnut shoots were treated with ABA, the NO donor sodium nitroprusside (SNP), ABA in combination with the NO scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (PTIO), PTIO, SNP in combination with the ABA biosynthesis inhibitor fluridone (Flu), and Flu. Their effects on chilling tolerance, reactive oxygen species (ROS) levels, and the antioxidant defense system were analyzed. The results showed that ABA treatment markedly alleviated the decreases in the maximal photochemical efficiency and survival and the increases in electrolyte leakage and lipid peroxidation induced by chilling stress, suggesting that application of ABA could improve the chilling tolerance. Further analyses showed that ABA enhanced antioxidant defense and slowed down the accumulation of ROS caused by chilling. Similar results were observed when exogenous SNP was applied. ABA in combination with PTIO or PTIO alone differentially abolished these protective effects of ABA. However, treatment with NO in combination with Flu or Flu alone did not affect the SNP-induced protective effect against CI or the activation of antioxidant activities under conditions of chilling stress. In addition, ABA treatment increased the NO content under chilling conditions, which was suppressed by the ABA biosynthesis inhibitor Flu or NO scavenger PTIO. Conversely, SNP application induced the same ABA rise observed in control plants in response to chilling. Taken together, these results suggested that ABA may confer chilling tolerance in walnut shoots in vitro by enhancing the antioxidant defense system, which is partially mediated by NO, preventing the overproduction of ROS to alleviate the oxidative injury induced by chilling.
Ningguang Dong, Jianxun Qi, Yuanfa Li, Yonghao Chen, and Yanbin Hao
Qi Wang, Rui Zhao, Qihang Chen, Jaime A. Teixeira da Silva, Liqi Chen, and Xiaonan Yu
Herbaceous peony is a perennial flowering plant with strong environmental adaptability and may be a good candidate for culture in arid areas. In this study, the physiological and biochemical responses of two herbaceous peony cultivars to different soil moisture gradients in pots were assessed by analyzing changes in 13 stress-related indices. The drought damage index (DDI) and the contents of malondialdehyde (MDA), soluble sugar, proline, and abscisic acid (ABA) generally increased as drought stress intensified, whereas leaf relative water content (LRWC) decreased, and the contents of soluble protein, indole-3-acetic acid (IAA), the ratio of IAA and ABA, and the activities of four antioxidant enzymes fluctuated. For the leaves, a positive correlation was found between DDI and superoxide dismutase (SOD), MDA, soluble sugar, proline, ascorbate peroxidase (APX), and ABA, but it was negatively correlated with LRWC, peroxidase (POD), and catalase (CAT). In fibrous roots, DDI was positively correlated with MDA, soluble sugar, proline, soluble protein, and ABA but was negatively correlated with SOD, CAT, APX, and IAA/ABA. Principal component analysis and subordinate functions were used to evaluate drought resistance of the two cultivars, with ‘Karl Rosenfield’ showing greater resistance to drought than ‘Da Fu Gui’.
Gojko Jelenkovic, Sharon Billings, Qi Chen, James Lashomb, George Hamilton, and Gerald Ghidiu
A population of 300 putative transgenic eggplants (Solanum melongena L.) carrying the syn cryIIIA gene was produced and tested for resistance to the Colorado potato beetle [CPB; Leptinotarsa decemlineata (Say)]. Toxicity tests in planta and in vitro demonstrated that 69% of the transformed plants were resistant to neonate larvae and adult CPB. Transgenicity of the plants was confirmed by studies of GUS expression and Southern and northern analysis. Primary transformants, having a single insert of the construct, upon selfing, produced progenies cosegregating for the uidA and syn cryIIIA genes at the expected 3:1 ratios with a few exceptions in which only one of the genes was expressed. The latter was attributed to the gene silencing phenomenon. The segregating resistant R1 seedlings showed the same level of resistance as the parental genotypes in growth chamber tests and under field conditions. One genotype carrying two copies of the construct, upon selfing, segregated at a 15:1 ratio for GUS expression and resistance to CPB, while Southern analysis revealed a 9:3:3:1 genotypic segregation ratio for individual copies of the construct.
Suxiao Hao, Yanfen Lu, Jing Liu, Yufen Bu, Qi Chen, Nan Ma, Zhiqin Zhou, and Yuncong Yao
Dwarfing rootstocks can improve the plant architecture of apple trees and increase production. Gibberellins (GAs) are crucial for plant growth and dwarfing traits. The receptor, GIBBERELLIN INSENSITIVE DWARF1 (GID1), plays an important role in the regulation pathway. However, the growth regulatory mechanism of GID1 in dwarf apple rootstock seedlings is not clear. In this study, we selected dwarf apple rootstock ‘SH6’ and its cross parents as materials to clone the GA receptor gene GID1c. There were two different sites in the alpha/beta hydrolase domain. The expression of GID1c in ‘SH6’ was lower than that in Malus domestica cv. Ralls Janet, with the decrease of GA content. We further conducted GA3 treatment and overexpression of GID1c in tissue culture seedlings of ‘SH6’, and the results showed that the expression of GID1c and biosynthesis genes increased and promoted the accumulation of hormone contents, which ultimately regulates the growth of ‘SH6’ dwarf apple rootstock seedlings. Our results suggest that GID1c may affect the plant architecture and dwarf traits of dwarfing rootstock and accelerate its application in orchards.
Qi Chen, Gojko Jelenkovic, Chee-Kok Chin, Sharon Billings, Jodi Eherhardt, Joseph C. Goffreda, and Peter Day
Three constructs of a coleopteran toxic cryIIIB Bacillus thuringiensis gene were engineered and incorporated into eggplant (Solanum melongena L.). Southern blot analysis of the eight primary transformants and segregational analysis of their R, progenies indicated that the chimeric cryIIIB constructs in each of the transgenic plants were stably incorporated at a single locus or at multiple sites within the same linkage group and that they were regularly transmissible to the progeny. The results of Northern blot and RNase protection analyses demonstrated that transcription of the cryIIIB mRNA takes place in plant cells, but only a small amount of the expected entire length transcripts were produced. The amount of the 5' end mRNA fragment produced was at least 30 to 40 times more abundant than the amount of the 3' end mRNA fragment. This could be interpreted to mean that either the two ends of the mRNA are of different stability or that the transcription process is often interrupted and only a few mRNAs complete the entire process to the end. When the transgenic plant mRNA was reverse-transcribed, amplified by polymerase chain reaction, and hybridized to the cryIIIB probe, two smaller molecular weight mRNA species were identified. Thus, the preponderance of the cryIIIB mRNA in transgenic plants exists as a truncated species, a situation similar to that of cryI genes when expressed in transgenic plants. Seedlings from the eight independent transgenic plants were tested for Coleopteran insect resistance. However, they did not demonstrate any significant resistance to the first and second instar larvae of the Colorado potato beetle (Leptinotarsa decemlineata Say).
Liang Zheng, Qi Zhang, Kexin Zheng, Shumei Zhao, Pingzhi Wang, Jieyu Cheng, Xuesong Zhang, and Xiaowen Chen
The application of diffuse light can potentially improve the homogeneity of light distribution and other microclimatic factors such as temperature inside greenhouses. In this study, diffuse light plastic films with different degrees of light diffuseness (20% and 29%) were used as the south roof cover of Chinese solar greenhouses to investigate the spatial distribution of microclimatic factors and their impacts on the growth and yield of tomato. The horizontal and vertical photosynthetic photon flux density (PPFD) distributions, air temperature distribution, and leaf temperature distribution inside the canopy, tomato leaf net photosynthesis (Pn), and fruit production during the growth period were determined. The results showed that diffuse light plastic film continuously improved the light distribution in the vertical and horizontal spaces of the crop canopy in terms of light interception and uniformity. A more diffuse light fraction also decreased the air and leaf temperatures of the middle canopy and upper canopy during the summer, thereby promoting the photosynthesis of the tomato plants. Pn of the middle and lower canopies with higher haze film were significantly greater than those with lower haze film (19.0% and 27.2%, respectively). The yields of higher stem density and lower stem density planted tomatoes in the 29% haze compartment were increased by 5.5% and 12.9% compared with 20% in the haze group, respectively. Diffuse light plastic films can improve the homogeneity of the canopy light distribution and increase crop production in Chinese solar greenhouses.
Yun-Peng Zhong, Zhi Li, Dan-Feng Bai, Xiu-Juan Qi, Jin-Yong Chen, Cui-Guo Wei, Miao-Miao Lin, and Jin-Bao Fang
To select resistant germplasm resources and understand the growth and physiological responses of kiwifruit (Actinidia sp.) to drought stress, five species, Actinidia macrosperma (Acma), Actinidia longicarpa (Aclo), Actinidia deliciosa (Acde), Actinidia hemsleyana (Ache), and Actinidia valvata (Acva), were assessed under tissue culture conditions. Rootless seedlings of five species were cultured in a medium containing polyethylene glycol [PEG (formula weight 8000)] to induce drought stress (0%, 5%, 10%, 15%, and 20%). After a 30-day culture, three growth indices [fresh weight (FW), plant height (PLH), and leaf number (LN)] and six physiological indices were determined, and the drought damage index (DDI) was determined. The DDIs of five species increased, and three growth indices decreased with increasing PEG concentrations. The following changes were observed under 20% PEG treatment conditions: superoxide dismutase (SOD) activities increased significantly in Acma, Aclo, and Ache specimens; peroxidase (POX) activities remained stable in Acde, Ache, and Acva specimens; and catalase (CAT) activities increased sharply in Acma and Acva. Furthermore, the results indicated that soluble sugar (SS) content increased slightly in Acma, Aclo, Acde, and Ache but it decreased in Acva specimens. Proline (PRO) content increased significantly in Acma and Acva, and malondialdehyde (MDA) contents tended to increase under drought stress in all five species. Principal component analysis (PCA) results indicated that the order of drought tolerance in the five genotypes examined in this study under tissue culture conditions was as follows: Acma > Acva > Acde > Aclo > Ache. Therefore, we concluded that Acma and Acva are more resilient germplasm resources that represent promising kiwifruit-breeding materials. Furthermore, tolerance to drought stress in these species should be further investigated under orchard conditions.