Ethylene-induced opposite redistributions of calcium and auxin are essential components in the development of tomato petiolar epinastic curvature

From a different angle: genetic diversity underlies differentiation of waterlogging-induced epinasty in tomato

In tomato, downward leaf bending is a morphological adaptation towards waterlogging, which has been shown to induce a range of metabolic and hormonal changes. This kind of functional trait is often the result of a complex interplay of regulatory processes starting at the gene level, gated through a plethora of signaling cascades and modulated by environmental cues. Through phenotypical screening of a population of 54 tomato accessions in a Genome Wide Association Study (GWAS), we have identified target genes potentially involved in plant growth and survival during waterlogging and subsequent recovery. Changes in both plant growth rate and epinastic descriptors revealed several associations to genes possibly supporting metabolic activity in low oxygen conditions in the root zone. In addition to this general reprogramming, some of the targets were specifically associated to leaf angle dynamics, indicating these genes might play a role in the induction, maintenance or recovery of differential petiole elongation in tomato during waterlogging.

Indoleacetic Acid Levels in Wheat and Rice Seedlings under Oxygen Deficiency and Subsequent Reoxygenation

The lack of oxygen and post-anoxic reactions cause significant alterations of plant growth and metabolism. Plant hormones are active participants in these alterations. This study focuses on auxin-a phytohormone with a wide spectrum of effects on plant growth and stress tolerance. The indoleacetic acid (IAA) content in plants was measured by ELISA. The obtained data revealed anoxia-induced accumulation of IAA in wheat and rice seedlings related to their tolerance of oxygen deprivation. The highest IAA accumulation was detected in rice roots. Subsequent reoxygenation was accompanied with a fast auxin reduction to the control level. A major difference was reported for shoots: wheat seedlings contained less than one-third of normoxic level of auxin during post-anoxia, while IAA level in rice seedlings rapidly recovered to normoxic level. It is likely that the mechanisms of auxin dynamics resulted from oxygen-induced shift in auxin degradation and transport. Exogenous IAA treatment enhanced plant survival under anoxia by decreased electrolyte leakage, production of hydrogen peroxide and lipid peroxidation. The positive effect of external IAA application coincided with improvement of tolerance to oxygen deprivation in the 35S:iaaM × 35S:iaaH lines of transgene tobacco due to its IAA overproduction.

Trans-aconitic acid inhibits the growth and photosynthesis of Glycine max

Grasses producing trans-aconitic acid, a geometric isomer of cis-aconitic acid, are often used in Glycine max rotation systems. However, the effects of trans-aconitic acid on Glycine max are unknown. We conducted a hydroponic experiment to evaluate the effects of 2.5-10 mM trans-aconitic acid on Glycine max growth and photosynthesis. The results revealed that the enhanced H2O2 production in the roots increased the membrane permeability and reduced the water uptake. These effects culminated with a reduced stomatal conductance (gs), which seems to be the main cause for a decreased photosynthetic rate (A). Due to low gs, the limited CO2 assimilation may have overexcited the photosystems, as indicated by the high production of H2O2 in leaves. After 96 h of incubation, and due to H2O2-induced damage to photosystems, a probable non-stomatal limitation for photosynthesis contributed to reducing A. This is corroborated by the significant decrease in the quantum yield of electron flow through photosystem II in vivo (ΦPSII) and the chlorophyll content. Taken together, the damage to the root system and photosynthetic apparatus caused by trans-aconitic acid significantly reduced the Glycine max plant growth.

Regulation of epinasty induced by 2,4-dichlorophenoxyacetic acid in pea and Arabidopsis plants

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) causes uncontrolled cell division and malformed growth in plants, giving rise to leaf epinasty and stem curvature. In this study, mechanisms involved in the regulation of leaf epinasty induced by 2,4-D were studied using different chemicals involved in reactive oxygen species (ROS) accumulation (diphenyleniodonium, butylated hydroxyanisole, EDTA, allopurinol), calcium channels (LaCl3), protein phosphorylation (cantharidin, wortmannin) and ethylene emission/perception (aminoethoxyvinyl glycine, AgNO3). The effect of these compounds on the epinasty induced by 2,4-D was analysed in shoots and leaf strips from pea plants. For further insight into the effect of 2,4-D, studies were also made in Arabidopsis mutants deficient in ROS production (rbohD, rbohF, xdh), ethylene (ein 3-1, ctr 1-1, etr 1-1), abscisic acid (aba 3.1), and jasmonic acid (coi 1.1, jar 1.1, opr 3) pathways. The results suggest that ROS production, mainly ·OH, is essential in the development of epinasty triggered by 2,4-D. Epinasty was also found to be regulated by Ca2+, protein phosphorylation and ethylene, although all these factors act downstream of ROS production. The use of Arabidopsis mutants appears to indicate that abscisic and jasmonic acid are not involved in regulating epinasty, although they could be involved in other symptoms induced by 2,4-D.