Plant Growth Regulation

Androgenesis is an important technique to generate double haploid plants. Anther and microspore cultures are the methods to induce haploid embryogenesis. For culture initiation, it is necessary to select anthers with the appropriate developmental stage of microspores. For lupins, limited reports about the establishment of initial cultures for androgenesis are available. In this study, different parameters of anther culture of three genotypes of Lupinus angustifolius were investigated. For all genotypes, a considerable correlation was observed between the buds and the anthers, depending on their location in the inflorescences. Buds from the central segment of inflorescences had yellowish green anthers that contained the maximum number of microspores at uninucleate stage. Cytological investigation shows that the anthers containing these microspores were the most responsive to induction. Two types of developmental pathways were observed for microspores. In case of cold pre-treated and untreated inflorescences, microspores developed into multicellular and embryo-like structures, respectively. Effects of different factors showed significant differences among: genotypes, pre-treatment, growth regulators (GRs) and genotypes × GRs interaction. Among three genotypes, Emir showed the highest number of multicellular and embryo-like structures on MS medium + 2.0 mg/l 2,4 D + 0.5 mg/l Kinetin (Kin). For all genotypes, anthers produced calli on MS medium containing 2.0 mg/l 2,4 D + 0.5 mg/l Kin. These calli continued their growth on regeneration medium (MS + 2.0 mg/l BA + 0.5 mg/l NAA) and produced roots. Taken together, these results provide a good basis for further research towards the development of haploid plants for L. angustifolius.

Diazocyclopentadiene (DACP) in the presence of fluorescent light delayed ripening of tomato fruits treated at the mature green (no visible red) stage. At 25 °C, ripening was delayed 10 days if DACP [185 µl/1 (gas)] was added as a single treatment and longer if DACP was added intermittently at 5-day intervals. The addition of 1000 µl/1 ethylene following DACP and light treatment did not hasten ripening. Little ripening delay was noted for fruit + DACP held in darkness. Tomatoes covered with aluminum foil so as to exclude light but not light-activated DACP, showed ripening inhibition. Apparently, the light-activated product from DACP is stable long enough to diffuse into fruit held in darkness. After an initial inhibition, ethylene production was greatly increased in tomatoes treated with DACP. Tomatoes with or without DACP treatment were held either in air or 5% O2/95% N2 for 12 days then treated with ethylene. Treatment with 5% O2 alone delayed ripening when compared to air alone, however, both groups reached 80% red color by 18 days. DACP treated fruit, whether held in air or 5% O2, still were green after 18 days and only approached 80% red color after approximately 27 days. Thus, 5% oxygen did not appear to slow the reversal of DACP inhibition of ripening.

We investigated the interaction between heat shock protein 70 (HSP70) and abscisic acid (ABA)-induced antioxidant response of maize to the combination of drought and heat stress. First, the increased activities of enzymes, including superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and catalase (CAT), induced by drought were less than those by heat or combined drought and heat stress, except some individual cases (e.g. CAT in leaves, GR in roots). Second, both HSP70 synthesis and H2O2 production increased prominently under drought, heat or their combination stress; the increase in leaves induced by drought and heat combination was the highest, followed by heat and by drought, while the increase in roots had not visible difference. Third, either in leaves or roots, pretreatment with ABA inhibitor, HSP70 inhibitor and H2O2 scavenger, significantly arrested the stress-induced increase of antioxidant enzyme activities, and ABA inhibitor and H2O2 scavenger obviously suppressed HSP70 synthesis, while HSP70 inhibitor slightly heightened H2O2 accumulation. Finally, 100 μM ABA significantly enhanced the activities of antioxidant enzymes, HSP70 expression and H2O2 production under stresses in comparison with ABA-deficient mutant vp5 maize plants without pretreatment. Thus, ABA-induced H2O2 production enhances the HSP70 synthesis and up-regulates the activities of antioxidant enzymes, resulting in the suppression of cellular reactive oxygen species (ROS) levels. Our results suggest that HSP70 may play a crucial role in ABA-induced antioxidant defense of maize to drought and heat combination.

The heading date of rice is a crucial agronomic traits affecting regional adaptation and grain productivity. Manipulating the vegetative growth period or delaying flowering can increase the yield and quality. The RICE FLOWERING LOCUS T (RFT1) has a critical role in flowering regulation. Here, we aimed to delay flowering in rice by reducing the expression of RFT1. For this purpose, we targeted four sites within the 0.5-kb region of RFT1 promoter for gene editing. Six homozygous mutant lines were obtained (rft1 pro-1 to rft1 pro-6), which showed delayed heading dates by 1.4–9.2 days. In addition, expression levels of Hd3a and RFT1 were significantly reduced, corroborating the late flowering phenotype. Using a dual-luciferase reporter in rice protoplast, we established that the protein level of LUC driven by the edited rft1 promoter was lower than that driven by the RFT1 promoter. In conclusion, we have developed a viable strategy to delay rice flowering by editing promoter of flower-promoting gene.

Phytohormones have been implicated in vascular development in various ways, but their precise function and the extent of their influence is still controversial. Recent results from experimental manipulation of developing organs and Arabidopsis developmental genetics support a role for polar auxin flow in cell axis formation within the vascular system and, interestingly, also in the embryonic establishment of the plant body axis. Vascular responses to auxin transport inhibition indicate patterns of auxin distribution during leaf development and new technologies may enable these predictions to be tested within the near future. Moreover, recently discovered Arabidopsis axialisation mutants seem to identify essential genes that relay auxin signals in vascular development. A first gene in this class, MONOPTEROS (MP) has been cloned and encodes a transcription factor capable of binding to auxin response elements in the control regions of auxin regulated genes. Molecular identification of further axialisation genes may provide access to a mechanistic understanding of plant cell axis formation.

Salicylic acid (SA) is involved in the salt-resistance of the halophyte plant species Solanum chilense. The SA analog 2,6-dichloroisonicotinc acid (INA) is commonly used to elicit SA signal transduction in response to biotic stress and is frequently used to confirm the SA involvement in plant response to pathogens. Data are lacking concerning its impact on plant response to salinity, especially in the halophyte species. Solanum chilense was cultivated in the absence or presence of 125 mM NaCl in nutrient solution and exposed to 0.01 mM exogenous SA or sprayed with 0.5 mM INA. Exogenous SA increased the shoot dry weight while INA did not. Exogenous INA, in contrast to SA, increased the shoot Na+ concentration in NaCl-treated plants and decreased the root K+ concentration. In the absence of salt, both SA and INA induced an increase in H2O2 which was not due to ascorbate peroxidase (EC 1.11.1.11) inhibition. In salt-treated plants, SA stimulated the ascorbate peroxidase activity while INA did not. Exogenous SA increased the root putrescine and spermidine concentrations while INA significantly decreased the concentration of these protecting compounds. It is concluded that exogenous SA and INA do not have similar impacts on the plant behavior and that the difference between these compounds may be influenced by NaCl. The use of INA as a reliable SA analog should therefore be considered with caution in halophyte plant species.

Corms of liatris (L. spicata, cv. Callilepsis) show a seasonal dormancy, being most active in the November harvest and least active in June. Storage of dormant corms at 3 °C for about 9 weeks resulted in a complete break of dormancy. This was accompanied by a sharp temporal increase in their rate of ethylene production, which was more pronounced in the buds than in the parenchyma tissue. Application of ethylene to the corms in the form of ethrel solution increased both ethylene production rate and sprouting. The ethylene-forming activity from ACC, measured both in vivo and in vitro, was higher in corms producing more ethylene. However, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) of the corms was inversely related to their ethylene production rate. Ethylene thus seems to be involved in the dormancy control of liatris corms, and its production is apparently regulated mainly by the activity of the membranous ethylene-forming system.

In rice, an E-class gene, OsMADS1, acts to specify the identities of the lemma and palea. In this study, the OsMADS1 gene with a CaMV35S promoter was transformed into a japonica cultivar, Zhonghua 11. All transgenic plants successfully showed similar phenotypes, including dwarfism, distorted panicles, decreased numbers of branches and spikelets, and elongated sterile lemma. Histological analysis showed that the elongated sterile lemma developed with silicified epidermal and sclerenchymal cells, which were lacking in the wild-type sterile lemma, suggesting that the elongated sterile lemma had assumed the identity of the lemma or palea. Some marker genes were subjected to a detailed analysis of the distribution of their expression among the lemma, palea and sterile lemma. DROOPING LEAF (DL) and OsMADS6 genes were only expressed in the normal lemma or palea, respectively. In the elongated sterile lemma, a high level of DL gene expression was detected, while no expression of OsMADS6 was found, implying that the sterile lemma transformed into the lemma but not the palea. These results provide clues to elucidate the mechanism of evolution from lemma to sterile lemma in rice. qPCR analysis also suggested that the ectopic expression of OsMADS1 induced abnormal brassinosteroid and gibberellin acid activation, and then resulted in developmental defects in the stem and panicle.