We used anti-indole-3-acetic acid (IAA) monoclonal antibodies to monitor the temporal and spatial pattern of IAA during pistillate flower bud differentiation in the walnut (Juglans regia) cultivar Liaoning 1. Based on morphological changes, the process of pistillate flower bud differentiation was divided into five stages. The flower induction stage, which includes the early phase, midphase, and late phase, persisted from 25 Apr. to the end of May. The pedicel differentiation stage began on 5 June. The bract primordium stage began on 25 June and persisted through mid-March of the next year. Both the perianth and pistil differentiation stages persisted for nearly 2 weeks. During the floral induction period, little IAA was present in the shoot apical meristem (SAM); hence, the SAM may not always be a site of IAA production. IAA was obviously concentrated in cells of the first several layers of the SAM during pedicel primordium formation. High levels of IAA were also noted in the phyllome, young leaf tips, and vascular bundle of leaves and gemmae. This direct evidence indicates that no close relationship exists between IAA and physiological differentiation; instead, IAA may strongly affect morphogenesis. These findings comprise a first step toward elucidating the walnut flowering mechanism.
Ying Gao, Hao Liu, Ningguang Dong, and Dong Pei
Ying Gao, Hao Liu, and Dong Pei
Monoclonal anti-indole acetic acid antibodies were used to monitor the temporal and spatial pattern of auxin during staminate flower differentiation in walnut (Juglans regia) cultivars Liaoning 1 and Liaoning 3. The relationship between morphological characteristics and histological structure was established. Seven stages of differentiation were recognized based on the visibility and color of the squama, bract, perianth, and rachis as follows: Stage 1, several bract primordia were present in the squama with catkins protruding from the squama as the only externally visible portion of the floret (Stage 1); the bract became externally visible, and the floret, perianth, and stamen primordia formed basipetally (Stage 2); the length of catkins were elongated, only bracts visible and getting brown (Stage 3); the bracts were brown and wrapped tightly, cellular specialization occurred to form a central core containing reproductive cells and tapetal cells that differentiated (Stage 4); the perianth became visible externally, reproductive cells and tapetal cells separated from the exterior layers of the anther wall (Stage 5); the anther walls were reduced to two cell layers (epidermis and endothecium) as the anthers became visible and matured (Stage 6); and the anther turned black, dehisced, and released its pollen grains (Stage 7). The histological differentiation of the flowers was related to auxin. The auxin signal was strongest in the shoot apical meristem (SAM) during bract primordia differentiation; thus, the SAM may be a site of auxin production. When the floral organs began centralized differentiation, auxin was distributed mainly in the differentiating tissues. Our findings indicate that a high level of auxin may strongly affect morphogenesis. Additionally, the tapetal and reproductive cells that arise during cellular specialization may be important for auxin production. The distribution of auxin was centralized in germ pores at the pollen grain surface, indicating that a high level of auxin induces pollen germination.
Lili Dong, Tongrui Liu, Di Gao, Jing Li, and Jie Qian
Petunia (Petunia ×hybrida) is an important ornamental plant, and its branch development has become a hot research topic. In this study, PhSDG8, an ortholog of SET domain group 8 (SDG8), was cloned from the petunia cultivar Mitchell Diploid. It had an open reading frame (ORF) of 5070 bp and encoded 1689 amino acids, with Suppressor variegation 3–9, Enhancer of zeste, Trithorax (SET), Zinc finger-cysteine and tryptophan conserved (Zf-CW), associated with SET (AWS) and Post SET domains. The predicted amino acid sequence of PhSDG8 was most closely related to Nicotiana sylvestris ASHH2 (NsASHH2). Expression analysis revealed that PhSDG8 expressed highest in the stems and lowest in the axil. Subcellular localization analysis showed that PhSDG8 was localized in the nucleus. Overexpression of PhSDG8 reduced the branch number of Arabidopsis thaliana sdg8-2. The silencing of PhSDG8 resulted in an increase in the number of branches of petunia and significant upregulation of PhUGT74E2. These results suggested that PhSDG8 may be a candidate gene for regulating the branching of petunia.
Lili Dong, Qi Wang, Feng Xiong, Na Liu, and ShuiMing Zhang
More axillary buds 1 (MAX1), initially identified in arabidopsis (Arabidopsis thaliana), is a key regulatory gene in strigolactone synthesis. CmMAX1, an ortholog of MAX1 was cloned from chrysanthemum (Chrysanthemum morifolium cv. Jinba). It had an open reading frame of 1611 bp and encoded 536 amino acid of P450 protein, with a conserved heme-binding motif of PFG × GPR × C × G, as well as PERF and KExxR motifs. The predicted amino acid sequence of CmMAX1 was most closely related to the MAX1 ortholog identified in lotus (Nelumbo nucifera), NnMAX1, with 55.33% amino acid sequence similarity. Expression analysis revealed there was no significant difference of CmMAX1 expression among various tissues. Phosphorus (P) deficiency significantly improved the expression levels of CmMAX1. Strigolactone, auxin, and cytokinin negatively regulated the expression of CmMAX1. Overexpression of CmMAX1 reduced the branch numbers of arabidopsis max1-1. These results suggest that CmMAX1 may be a candidate gene for reducing the shoot branching of chrysanthemum.
Xiao-min Liu, Xin-zhi Zhang, Yi-min Shi, and Dong-qin Tang
Genetic diversity of Narcissus was systematically studied on both morphological and molecular levels. Twenty-four characteristics of nine narcissi were observed and their differences evaluated by clustering method. The results showed that nine narcissi can be divided into two subclusters: one comprised by Narcissus pseudonarcissus, the other by Chinese Narcissus. The morphological diversity among five cultivars of N. pseudonarcissus is higher than that among four ecotypes of Chinese Narcissus (Narcissus tazetta var. chinensis). There are seven morphological characteristics in N. pseudonarcissus presenting obvious variations with coefficients from 33.33% to 91.67%. Only five morphological characteristics in Chinese Narcissus present certain variations with coefficients from 37.04% to 51.79%. On DNA level, two clusters are distantly related too. Based on the random amplified polymorphic DNA (RAPD) markers, 13 out of 40 random primers yielded scorable polymorphisms between samples. Wide variations in banding profiles between cultivars or between ecotypes were observed with nearly every primer tested. Among 95 band positions that were scored for all the 9 narcissi, 81 are polymorphic (85.26%). Cluster analysis of the calculated similarity matrix revealed that the genetic diversity between these individuals within the same section is low. However, the genetic diversity between two sections is obviously higher. Taken together, the methods combined morphological characteristics and RAPD technique allow a deep evaluation of the variation of Narcissus on both section level and cultivar/ecotype level.
Frederic Ngezahayo, Wanli Guo, Lei Gong, Fangxia Li, Bao Liu, and Yingshan Dong
The authors have previously reported an efficient in vitro system for mass micropropagation of Robinia ambigua `idahoensis' (Idaho locust). Their method used enhanced branching of axillary buds from a single donor plant along with detection of somaclonal variation by the intersimple sequence repeat (ISSR) markers. Because ISSRs tend to be clustered to specific chromosomal regions in plant genomes, the extent and scope of the genomic variations and the sequences underlying the variation warranted further investigations. In this study, the authors analyzed the same set of 40 randomly selected micropropagated R. ambigua plants by a more general molecular marker—random amplified polymorphic DNA (RAPD) using 34 selected primers. In addition, they sequenced some of the variable bands. Of the 260 reproducible RAPD bands scored, 70 were polymorphic among the 41 plants (40 micropropagated and one donor), corresponding to a polymorphism level of 26%. Cluster analysis revealed a genetic similarity ranging from 0.61 to 0.97. Of the 20 sequenced bands underlying the variations, eight showed significant homology to known or predicted functional cellular genes or retroelements. These results clearly indicated that micropropagation of R. ambigua, even by enhanced branching of axillary buds, can be accompanied by extensive genomic variations, which should be taken into account for commercial propagation of this plant by in vitro means.
De-Kun Dong, Jia-Shu Cao, Kai Shi, and Le-Cheng Liu
To investigate the genetic basis of heterosis in Brassica rapa, an F2 population was produced from the cross of B. rapa L. subsp. chinensis (L.) Hanelt and B. rapa L. subsp. rapifera Metzg. Trait performances of the F1 hybrid showed evident mid parent heterosis, which varied from 18.55% to 101.62% for the 11 traits investigated. A total of 23 main effect quantitative trait loci (QTLs) were detected for biomass and its component traits, which could explain 4.38% to 47.80% of the phenotypic variance, respectively. Sixty-five percent of these QTLs showed obvious overdominance. Epistasis analysis detected 444 two-locus interactions for the 11 traits at the threshold of P < 0.005. Some of them remained significant when more stringent threshold were set. These results suggested that overdominance and epistasis might play an important role as the genetic basis of heterosis in B. rapa.
Ping Li, Dong Liu, Min Guo, Yuemin Pan, Fangxin Chen, Huajian Zhang, and Zhimou Gao
Sexual reproduction in the plant parasite Phytophthora capsici Leonian requires the interaction of two distinct mating types, A1 and A2. Co-occurrence of these mating types can enhance the genetic diversity of P. capsici and alter its virulence or resistance characteristics. Using an intersimple sequence repeat (ISSR) screen of microsatellite diversity, we identified, cloned, and sequenced a novel 1121-base pair (bp) fragment specific to the A1 mating type of P. capsici. Primers Pcap-1 and Pcap-2 were designed from this DNA fragment to specifically detect the A1 mating type. Polymerase chain reaction (PCR) using these primers amplified an expected 997-bp fragment from known A1 mating types, but yielded a 508-bp fragment from known A2 mating types. This PCR-based assay could be adapted to accurately and rapidly detect the co-occurrence of A1 and A2 P. capsici mating types from field material.
Guang-Lian Liao, Xiao-Biao Xu, Qing Liu, Min Zhong, Chun-Hui Huang, Dong-Feng Jia, and Xue-Yan Qu
Jinyan (Actinidia eriantha × A. chinensis) is one of the gold-fleshed kiwifruit cultivars currently being promoted in south China. However, its fruit dry matter is usually less than 16%, which seriously affects fruit quality including taste and flavor. This causes a financial loss to growers: not only are the prices paid for the fruit low because of their bad reputation for quality, but some orchards have been removed. Improvement of fruit quality is essential. In this study, a method is described for squeezing and twisting flowering shoots before flowering and removing the distal vegetative parts of flowering shoots after fruit set. The effects on fruit quality were determined. The dry matter of fruit was increased by 6.6%. Fruit size also increased as did the chlorophyll a content and the chlorophyll:carotenoid ratio. The significantly increased fruit dry matter, resulting in significant increases in fruit soluble solids concentrations (P < 0.01), thereby possibly improving fruit taste. Fruit weight, fruit length, and carotenoid and ascorbic acid concentrations were significantly enhanced in comparison with controls (P < 0.01), increasing by 20%, 7%, 12%, and 19%, respectively. However, there was no significant difference in soluble sugar concentrations, titratable acid concentrations, and the reduced chlorophyll b concentrations. This research provides a practical method to increase fruit dry matter, and hence a way to allow fruit quality to reach commercial requirements for cultivars such as Jinyan, which under previous management systems had significant shortcomings in fruit flavor and taste.
Rui Zhang, Fang-Ren Peng, Pan Yan, Fan Cao, Zhuang-Zhuang Liu, Dong-Liang Le, and Peng-Peng Tan
Root systems of pecan trees are usually dominated by a single taproot with few lateral roots, which are commonly thought to inhibit successful transplanting. This study aimed to evaluate early growth and root/shoot development of pecan seedlings in response to taproot pruning. Taproots of ‘Shaoxing’ seedling pecan trees were mildly (1/3 of the total length of the radicle removed) and severely (2/3 of the total length of the radicle removed) pruned at different seedling development stages shortly after germination. At the end of the first growing season, top growth was measured and then trees were uprooted so that root system regrowth could be evaluated. The results showed that root pruning had no impact on increases in stem height or stem diameter. However, pruning the taproot could stimulate primary growth in taproot branches. Root weight and the number of taproot branches per tree increased with decreasing taproot length. This study indicated that severe root pruning when three to five leaves had emerged resulted in root systems with more taproot branches and the greatest root dry weight after one growth season, which may increase survival and reduce transplanting shock.