Plant Growth Regulation

Light quality and the cell-growth-related proteins called expansins (EXPs) are two crucial factors in plant growth and development. However, molecular insights into the light responses of EXPs and the influences of light-dependent EXP expression changes on plant growth and development remain scarce. A preliminary analysis using a cDNA microarray revealed that red, blue, violet, and far-red light emitting diode (LED) light exposure and dark periods differentially regulate the expression of 27 Brassica rapa EXPs (BrEXPs). The results indicated that photosynthetically significant red and blue light induce the expression of BrEXPA1, and these results were further confirmed using a semi-qRT-PCR assay. The identification of several light-responsive cis-regulatory elements in the BrEXP promoter sequences suggested that light signals were perceived through these promoter motifs to regulate the gene expression that eventually controls growth and development. To substantiate our hypothesis that the light-dependent regulation of EXPs modulates growth and development, we developed transgenic reporter lines of B. rapa expressing GUS under the BrEXPA1 promoter. A histochemical analysis showed that BrEXPA1-promoter-driven GUS activity was prominent in the leaves, radicles, lateral roots, and flowers of plants grown under monochromatic red or blue light. The biological functions of BrEXPA1 were further tested by overexpressing sense (OE-S) and antisense BrEXPA1 (OE-AS) transcripts in Arabidopsis. The OE-S lines displayed long radicles, wide leaves, and additional rosette leaves compared to the controls, whereas the OE-AS lines exhibited early bolting. Collectively, our results demonstrated the relationship between light and BrEXPs and also the light-dependent role of BrEXPA1 in growth regulation.

Changes in soluble carbohydrate composition and concentration in leavesand petioles of watermelon (Citrullus lanatus (Thunb)Matsum and Nakai cv. Sugar Baby) seedlings during early stages ofphytochrome-regulated petiole elongation were investigated. Watermelon seedlingswere grown in a controlled environment with 350 μmolm−2 s−1 photosynthetically activeradiation (PAR) during a 12-h photoperiod. Low intensity end-of-day(EOD) light treatments (for 15 min) of red (R), far-red (FR) and FRfollowed by R (FR/R) were initiated when the seedlings were 14 days old.Seedling growth, and soluble carbohydrate concentration and composition inleaves and petioles were determined after 3 and 6 days of EOD light treatments.The EOD FR increased the petiole length and dry mass partitioned to petioles asearly as 3 days into the treatment. This increased petiole dry mass inFR-treated plants was accompanied with an increase in reducing sugar (glucoseand fructose) concentration in the petioles. Although both leaves and petiolesshowed this effect, the relative increase was greater in petioles than leaves.While the most abundant sugars in petioles were fructose and glucose, thepredominant sugars in leaves were sucrose, raffinose, and stachyose. Thephotoreversion of FR induced changes in growth and sugar concentrations by Rindicates the involvement of phytochrome in these processes.

A transcription factor (TF) is a protein that binds to specific DNA sequences and thereby controls transcription. A large number of TFs are found in plants. The AP2/ERF family of TFs contain the AP2 DNA-binding domain, which play important roles in transcriptional regulation in plant life. To understand the AP2/ERF family TFs of maize, the discovery, phylogeny and expression pattern analysis of AP2-like genes from maize were described. A total of 167 AP2-like genes were identified by in silico cloning using the amino acid sequence of AP2/ERF family TFs from Arabidopsis thaliana as the probe. The maize AP2-like genes identified were orthologous to those TFs in Arabidopsis. The AP2/ERF TFs from maize were classified into four subfamilies (DREB, ERF, AP2 and RAV) and a Soloist. Using the EST information of maize as a source of expression data, those AP2-like genes from maize were detected in different plant tissues.

A cold pretreatment is usually applied to induce maize androgenesis. Peroxidase activity, including indole-3-acetic acid (IAA) oxidase activity, and endogenous IAA concentrations were followed during a cold pretreatment (14 days, 7°C) in anthers of two maize genotypes, Seneca 60 and DH5×DH7, respectively with a low or high androgenetic response. The most prominent result was the absence of a detectable IAA oxidase activity in DH5×DH7. Adding effectors of IAA-oxidase activity or IAA transport did not affect significantly the crude peroxidase activity of DH5×DH7 anthers while inducing a clear inhibition of androgenesis at higher concentrations. No strict correlation was found between IAA level and physiological response, the low responding variety having as much IAA as DH5×DH7. However, for DH5×DH7, every treatment that lowered the IAA level after 14 days of cold resulted in a decrease in androgenetic response.

Ảnh hưởng của một loại nấm nội sinh, Fusarium mairei, đến sự phát triển và hình thành paclitaxel của tế bào Taxus cuspidata đã được nghiên cứu bằng cách thêm dịch khối văn hóa nấm nội sinh (FECS) vào các môi trường nuôi cấy treo của tế bào T. cuspidata. Chất hóa học chính có tác dụng trong việc hình thành paclitaxel trong FECS là một exopolysaccharide (EPS) có khối lượng phân tử khoảng 2 kDa. Các phần tử của FECS ngoại trừ EPS thúc đẩy sự phát triển của tế bào Taxus nhưng không có tác động đến sự tích lũy paclitaxel. Ngoài ra, hiệu quả kích thích của FECS dựa trên các điều kiện nuôi cấy khác nhau cũng đã được nghiên cứu. Thành phần EPS trong FECS có liên quan đến các điều kiện nuôi cấy của FECS. FECS với thời gian nuôi cấy dài và điều kiện cấp dưỡng oxy cao chứa nhiều EPS hơn và tạo ra năng suất paclitaxel cao hơn so với FECS có thời gian nuôi cấy ngắn và điều kiện cấp dưỡng oxy thấp. Năng suất tối đa của paclitaxel từ các môi trường nuôi cấy Taxus, được kích thích bởi FECS với thời gian nuôi cấy 9 ngày, cao gấp 4,7 lần so với các môi trường đối chứng.

In ungerminated rice seeds, (Japonica rice variety, CV Tapei 309), the content of free amines (putrescine, spermidine, spermine, tyramine) was higher in seed lots having a low germination frequency compared to those with high germination potential. Conversely, amine conjugates (di-feruloylputrescine, di-feruloylspermidine, diferuloyldiaminopropane and feruloyltyramine) decreased with loss of viability. Thus, these compounds appeared to constitute biochemical markers of seed viability. In seeds with high germination potential, conjugates decreased drastically during germination, with an early and rapid increase in free amines (putrescine, spermidine, tyramine). Arginine decarboxylase (ADC) activity was highest during the germination of high germination potential seeds, its activity gradually declining with loss of viability and being closely correlated with agmatine content. The polyamine biosynthetic inhibitors (α-DL-difluoromethylarginine, DFMA, a specific and irreversible inhibitor of ADC; α-DL-difluoromethylornithine, DFMO, a specific irreversible inhibitor of ornithine decarboxylase (ODC); cyclohexylammonium sulfate, CHA, inhibitor of spermidine synthase) neither depleted putrescine and spermidine levels nor inhibited germination in high germination potential seeds. In low germination potential seeds, the germination process was inhibited by DFMA or CHA. Application of agmatine resulted in a reversal of inhibition. DFMA inhibited ADC activity in both categories of seeds. In low germination potential seeds treated with CHA no ADC activity was found. These results suggest that amines are involved in the germination process of rice seeds. It appears that amine conjugates may serve as a storage form of amines which, upon enzymatic hydrolysis, could supply the cell with an additional amine reserve and influence cell division and/or cell elongation.