Mesophyll Abscisic Acid Restrains Early Growth and Flowering But Does Not Directly Suppress Photosynthesis

Abstract

Abscisic acid (ABA) levels increase significantly in plants under stress conditions, and ABA is thought to serve as a key stressresponse regulator. However, the direct effect of ABA on photosynthesis and the effect of mesophyll ABA on yield under both well-watered and drought conditions are still the subject of debate. Here, we examined this issue using transgenic Arabidopsis (Arabidopsis thaliana) plants carrying a dominant ABA-signaling inhibitor under the control of a mesophyll-specific promoter (FBPase::abi1-1, abbreviated to fa). Under normal conditions, fa plants displayed slightly higher stomatal conductance and carbon assimilation than wild-type plants; however, these parameters were comparable following ABA treatment. These observations suggest that ABA does not directly inhibit photosynthesis in the short term. The fa plants also exhibited a variety of altered phenotypes under optimal conditions, including more vigorous initial growth, earlier flowering, smaller flowers, and delayed chlorophyll degradation. Furthermore, under optimal conditions, fa plant seed production was less than a third of that observed for the wild type. However, under drought conditions, wild-type and fa seed yields were similar due to a significant reduction in wild-type seed and no reduction in fa seed. These findings suggest that endogenous basal ABA inhibits a stress-escape response under nonstressed conditions, allowing plants to accumulate biomass and maximize yield. The lack of a correlation between flowering time and plant biomass combined with delayed chlorophyll degradation suggests that this stress-escape behavior is regulated independently and upstream of other ABA-induced effects such as rapid growth and flowering.

Wide vessels sustain marginal transpiration flux and do not optimize inefficient gas exchange activity under impaired hydraulic control and salinity

“…The widely cultivated commercial tomato ( Solanum lycopersicum L) variety M82 was studied as wild type line (WT). A population of T 1 transgenic tomato containing the insertion of the abi1‐1 Arabidopsis mutant gene under the FBPase promoter (FBPase:: abi1‐1 ; Negin et al ) was grown under selection conditions (Kanamycin spraying). The population was scanned and a single transgenic type (TT) was selected for further examination.…”

Signaling mechanisms in abscisic acid‐mediated stomatal closure

“…As discussed earlier, ABA signaling has been reported to downregulate signal transduction by the TOR protein kinase (Wang et al ., 2018c). Further research will be needed to determine whether basal ABA and/or the increase in plant growth and the alteration of metabolism in ABA‐deficient mutants and ABA signaling mutants under non‐stress conditions (Negin et al ., 2019; Yoshida et al ., 2019b) could result from enhanced TOR signaling.…”

Stress is basic: ABA alkalinizes both the xylem sap and the cytosol of Arabidopsis vascular bundle sheath cells by inhibiting their P-type H+-ATPase and stimulating their V-type H+-ATPase

“…Bundle-sheath-ABA-insensitive (SCR:abi1-1) plants were constructed similarly to fa plants of (Negin et al, 2019). Briefly, the abi1-1 gene (Koornneef et al, 1984) and the SCR promoter were cloned into pDONR plasmids and then inserted into the binary pB7M24GW (Invitrogen) plasmid.…”

“…Quantification of abi1-1 expression in WT, abi1-1 and SCR:abi1-1 plants by restriction enzymes was as described by (Negin et al, 2019). Briefly, total RNA was extracted from leaves and cDNA was prepared.…”