Comparative study of the cell wall composition of broccoli, carrot, and tomato: structural characterization of the extractable pectins and hemicelluloses

This study delivers a comparison of the pectic and hemicellulosic cell wall polysaccharides between the commonly used vegetables broccoli (stem and florets separately), carrot, and tomato. Alcohol-insoluble residues were prepared from the plant sources and sequentially extracted with water, cyclohexane-trans-1,2-diamine tetra-acetic acid, sodium carbonate, and potassium hydroxide solutions, to obtain individual fractions, each containing polysaccharides bound to the cell wall in a specific manner. Structural characterization of the polysaccharide fractions was conducted using colorimetric and chromatographic approaches. Sugar ratios were defined to ameliorate data interpretation. These ratios allowed gaining information concerning polysaccharide structure from sugar composition data. Structural analysis of broccoli revealed organ-specific characteristics: the pectin degree of methoxylation (DM) of stem and florets differed, the sugar composition data inferred differences in polymeric composition. On the other hand, the molar mass (MM) distribution profiles of the polysaccharide fractions were virtually identical for both organs. Carrot root displayed a different MM distribution for the polysaccharides solubilized by potassium hydroxide compared to broccoli and tomato, possibly due to the high contribution of branched pectins to this otherwise hemicellulose-enriched fraction. Tomato fruit showed the pectins with the broadest range in DM, the highest MM, the greatest overall linearity and the lowest extent of branching of rhamnogalacturonan I, pointing to particularly long, linear pectins in tomato compared with the other vegetable organs studied, suggesting possible implications toward functional behavior.     

Atnoa1 mutant Arabidopsis plants induce compensation mechanisms to reduce the negative effects of the mutation

Alterations in temperature adaptation processes and changes in the content of stress-related compounds, polyamines and salicylic acid were evaluated in Atnoa1 (NO-associated 1) Arabidopsis mutant. The F_v/F_m chlorophyll-a fluorescence induction parameter and the actual quantum yield were significantly lower in the Atnoa1 mutant than in the wild-type. In the wild-type Col-0, the fastest increase in the non-photochemical quenching (NPQ) occurred in plants pre-treated at low temperature (4 °C), while the slowest was in those adapted to 30 °C. The NPQ showed not only a substantially increased level in the light-adapted state, but also more rapid light induction after the dark-adapted state in the Atnoa1 mutant than in the wild-type. The results of freezing tests indicated that both the wild-type and the mutant had better freezing tolerance after cold hardening, since no significant differences were found between the genotypes. The level of putrescine increased substantially, while that of spermine decreased by the end of the cold-hardening (4 °C, 4 d) period. The quantity of spermidine in Atnoa1 was significantly higher than in Col-0, at both control and cold-hardening temperatures. A similar trend was observed for spermine, but only under control conditions. The mutant plants showed substantially higher salicylic acid (SA) contents for both the free and bound forms. This difference was significant not only in the control, but also in the cold-hardened plants. These results suggest that there is a compensation mechanism in Atnoa1 mutant Arabidopsis plants to reduce the negative effects of the mutation. These adaptation processes include the stimulation of photoprotection and alterations in the SA and polyamine compositions.     

Mutations in two putative phosphorylation motifs in the tomato pollen receptor kinase LePRK2 show antagonistic effects on pollen tube length

The tip-growing pollen tube is a useful model for studying polarized cell growth in plants. We previously characterized LePRK2, a pollen-specific receptor-like kinase from tomato (1). Here, we showed that LePRK2 is present as multiple phosphorylated isoforms in mature pollen membranes. Using comparative sequence analysis and phosphorylation site prediction programs, we identified two putative phosphorylation motifs in the cytoplasmic juxtamembrane (JM) domain. Site-directed mutagenesis in these motifs, followed by transient overexpression in tobacco pollen, showed that both motifs have opposite effects in regulating pollen tube length. Relative to LePRK2-eGFP pollen tubes, alanine substitutions in residues of motif I, Ser(277)/Ser(279)/Ser(282), resulted in longer pollen tubes, but alanine substitutions in motif II, Ser(304)/Ser(307)/Thr(308), resulted in shorter tubes. In contrast, phosphomimicking aspartic substitutions at these residues gave reciprocal results, that is, shorter tubes with mutations in motif I and longer tubes with mutations in motif II. We conclude that the length of pollen tubes can be negatively and positively regulated by phosphorylation of residues in motif I and II respectively. We also showed that LePRK2-eGFP significantly decreased pollen tube length and increased pollen tube tip width, relative to eGFP tubes. The kinase activity of LePRK2 was relevant for this phenotype because tubes that expressed a mutation in a lysine essential for kinase activity showed the same length and width as the eGFP control. Taken together, these results suggest that LePRK2 may have a central role in pollen tube growth through regulation of its own phosphorylation status.     

‘津田’芜菁Transparent Testa Glabra 1（BrTTG1）基因的克隆及表达分析

TTG1（Transparent Testa Glabra 1）蛋白是一种WD40类蛋白,参与植物的生长和发育。采用RT-PCR方法从芜菁品种‘津田＇中克隆了BrTTG1 cDNA序列（GenBank登录号HM208590）。该基因cDNA开放阅读框长度为1 014 bp,编码一个由337个氨基酸残基组成的蛋白,该蛋白分子量为37.28 kDa,理论等电点为4.66。与其他植物中的TTG1蛋白进行同源性比对结果显示,BrTTG1与甘蓝型油菜的TTG1同源性最高。BrTTG1蛋白在31～337位氨基酸处含有WD40超家族的保守结构域。荧光定量PCR检测BrTTG1在‘津田＇芜菁不同组织中的表达结果表明,该基因在有花青素合成的红色‘津田＇芜菁根皮中表达量最高。     

Molecular Detection and Complete Genome Sequences of Tomato chlorosis virus Isolates from Infectious Outbreaks in China

Tomato chlorosis virus (ToCV) is a whitefly‐transmitted, phloem‐limited, bipartite Crinivirus. In 2012, severe interveinal symptoms characteristic of ToCV infections were observed in greenhouse tomato plants in the Shandong province of China. High levels of infestation by whiteflies (Bemisia tabaci), which transmit ToCV, were also observed on tomato plants in all the greenhouses investigated. The presence of ToCV was confirmed by specific RT‐PCR either in the sampled plants or in the whiteflies collected from the ventral surface of the leaves of diseased plants. The complete genomic nucleotide sequences (RNA1 and RNA2) of the Shandong isolate of ToCV (ToCV‐SDSG) were determined and analysed. ToCV‐SDSG RNA1 consisted of 8594 nucleotides encompassing four open reading frames (ORFs). ToCV‐SDSG RNA2 consisted of 8242 nucleotides encompassing nine ORFs. Phylogenetic analysis suggests that the Chinese ToCV‐SDSG isolate is most similar to the ToCV‐Florida isolate.     

Biocontrol of Rhizoctonia solani damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of Algerian Sahara

Thirty-four endophytic actinomycetes were isolated from the roots of native plants of the Algerian Sahara. Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomyces genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently tested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils, and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seeds with antagonistic isolates significantly reduced (P < 0.05) the severity of damping-off of tomato seedlings. Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction as thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P < 0.05) were observed. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling length and the root length of the seed-treated seedlings compared to the control. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2 were related to Streptomyces mutabilis NBRC 12800^T (100% of similarity) and Streptomyces cyaneofuscatus JCM 4364^T (100% of similarity), respectively.     

3个香榧单株的种实性状变异分析

对浙江宁海3个香榧单株种实种长、种径、种长径比(种形系数)、单种重、鲜出核率、核长、核径、核长径比(核形指数)、单核重9个性状指标进行了测定和统计分析,为香榧优株选育提供理论依据。结果表明:单种重平均值最大的是宁榧1号(9.17 g),单种重极大值出现在宁榧1号(13.6 g);单核重平均值最大的为宁榧1号(2.93 g)。平均鲜出核率最大的是宁榧3号,达到40.86%,鲜出核率极大值出现在宁榧2号(51.06%)。株间种长、种径、种长径比、核长、核长径比、单种重、单核重、鲜出核率指标均存在显著差异,而核径差异性不显著。种实性状变异幅度最大的指标为单核重(变异系数CV为22.68%),单种重(变异系数CV为21.18%)次之,最小的为种长径比(变异系数CV为4.49%)。种长、种径、核长、核径均与单种重和单核重有显著相关性,鲜出核率与种长、种径、单种重、呈极显著负相关,与种长径比呈极显著正相关。     

Intraguild predation and sublethal interactions between two zoophytophagous mirids,Macrolophus pygmaeus and Nesidiocoris tenuis

The omnivorous predators Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae) are important biological control agents of pests on tomato crops. In this study, potential intraguild predation (IGP) interactions between the two species were investigated on tomato. We examined: (a) the within plant distribution of both species in the field, (b) the within plant distribution of each predatory species when co-occurred at high densities on tomato caged plants, (c) their behavioral interactions when enclosed in experimental arenas and (d) the development young and old nymphs of M. pygmaeus when enclosed together with N. tenuis adults. Results revealed that the two predators showed a different distribution pattern on the plants, with N. tenuis exploiting mostly the upper part, whereas M. pygmaeus were mostly observed on the 5th to the 7th leaf from the top. However, when the predators co-occurred, N. tenuis or M. pygmaeus individuals were recorded with increased numbers on the lower or the higher part of the plant, respectively. In the presence of N. tenuis adult young nymphs of M. pygmaeus completed their development to the adult stage, when alternative prey (lepidopteran eggs) was present on the plant, however failed to reach adulthood in the absence of alternative prey. A high percentage of the dead nymphs found with their body fluids totally sucked indicating predation by N. tenuis. However, large 4th instar nymphs of M. pygmaeus were much less vulnerable to N. tenuis than younger. The behavior of N. tenuis was affected by the presence of M. pygmaeus, but at a rate similar to that when two individuals of N. tenuis were enclosed together. Contacts between the predators were recorded in a similar frequency in mono- and heterospecific treatments, whereas aggressive behavior was not observed. This study shows that intraguild interactions between M. pygmaeus and N. tenuis occur but are not intensive. The potential implications of the outcomes for biological control are discussed.     

鲜食番茄果实中番茄红素含量的主基因－多基因混合遗传分析

选择2个番茄红素含量显著不同的鲜食番茄品系,通过P₁、P₂、F₁、F₂、B₁和B₂6世代联合分析法,研究分析了番茄红素的遗传规律。结果表明：番茄红素的遗传符合一个主基因和加性－显性－上位性多基因模型,主基因遗传力在B₁、B₂和F₂分别为6.85%、34.78％和58.33％,多基因遗传力在B₁、B₂和F₂分别为58.48％、30.69％和0。