Plants lacking OST1 show conditional stomatal closure and wildtype‐like growth sensitivity at high VPD

Abstract

Climate change‐associated rise in VPD (atmospheric vapor pressure deficit) results in increased plant transpiration and reduced stomatal conductance, photosynthesis, biomass, and yield. High VPD‐induced stomatal closure of Arabidopsis is an active process regulated via the kinase SnRK2.6 (OPEN STOMATA 1, OST1). Here, we performed gas exchange, leaf water potential and rosette growth measurements to study, whether (1) high VPD‐induced stomatal closure is detected in plants carrying loss‐of‐function mutations in OST1 (ost1‐3) when they are grown at reduced soil water content or measured at increased air temperature; (2) ost1‐3 plants expressing OST1 construct with no ABA‐activation domain, but intact ABA‐independent activation, show stronger stomatal VPD response compared with ost1‐3 plants; and (3) rosette area and biomass of ost1‐3 are more affected by growth at high VPD compared with Col‐0. The stomata of well‐watered ost1‐3 plants were insensitive to high VPD regardless of air temperature, but in deficit‐irrigated ost1‐3, leaf water potential decreased the most and stomata closed at high VPD. Differences between VPD‐induced stomatal closures of ost1‐3 plants and ost1‐3 plants expressing OST1 with no ABA‐activation domain point at gradual VPD‐induced ABA‐independent activation of OST1. High VPD conditions led to similar reductions in rosette area and specific leaf area of well‐watered Col‐0 and ost1‐3 plants. Rosette dry mass was unaffected by high VPD. Our results show that OST1 loss‐of‐function plants display conditional stomatal closure and no extra sensitivity of rosette area growth compared with Col‐0 wildtype under high VPD conditions.

Low relative air humidity and increased stomatal density independently hamper growth in young Arabidopsis

“…2015). However, in our recent study, growth under low RH was not more impaired in the ost1 mutant with large stomatal conductance than in wild-type plants (Tulva et al . 2023).…”

“…Experiments addressing the effects of low air humidity help to address the role of increased evaporative demand on plant growth. Low night-time relative humidity did not affect biomass production in Arabidopsis (Christman, Donovan & Richards 2009), whereas we recently found that low air humidity applied both during the day and night hampered plant growth in both wild-type plants and mutants with increased stomatal conductance due to larger stomatal apertures (Tulva, Välbe & Merilo 2023).…”

Passive stomatal closure under extreme drought in an angiosperm species

“…There are a few reasons why passive stomatal closure during drought in angiosperms is not widely accepted, the first is that mutants of ABA biosynthesis and signalling do not close effectively during drought or when leaf water status changes (Brodribb et al 2021;Tulva et al 2023), suggesting that if there is a passive regulation of stomatal response to leaf water status in species from this group of land plants it is minor or ineffective. Stomatal responses to short-term changes in leaf water status induced by vapour pressure difference between the leaf and the atmosphere (VPD) in angiosperms are not predictable by a passive-hydraulic model whereby guard cell turgor is linked to leaf turgor (Binstock et al 2023;Cardoso et al 2020).…”