S11 - Session O3 - Tomato plants with different endogenous ABA levels show unique phenotypic and phytohormones response to elevated CO2 and progressive soil drying

Authors: Kehao Liang *, Fulai Liu

Increasing atmospheric CO 2 concentration accompanied by drought stress have a significant impact on plant performance. Our previous study showed that elevated CO 2 ( e [CO 2 ]) can stimulate net photosynthetic rate (A n ) and depress stomatal conductance (g s ) in wild-type tomato ( Solanum lycopersicum ), and retard the response of g s to progressive soil drying. This study aimed to investigate the effect of e [CO 2 ] on the responses of leaf gas exchange, plant water relations, phenotypic adjustment and ethylene evolution of tomato plants with different endogenous ABA levels to progressive soil drying. Wild type genotype Ailsa Craig (AC), its ABA-deficient mutant ( flacca ) and transgenic tomato sp5 (over-expressing NCED1 gene, thus improving endogenous ABA concentrations) were examined. At onset of drought, e [CO 2 ] increased the A n in flacca and sp5, but not in AC. Compared to ambient CO 2 ( a [CO 2 ]), e [CO 2 ] decreased g s in AC and sp5, and retarded stomatal closure only in sp5 during soil drying. Under drought, e [CO 2 ] improved leaf water use efficiency in all genotypes and relatively better maintained leaf water potential except in the flacca mutant. CO 2 , drought and genotypes have an interactive effect on the specific leaf area (SLA); after soil drying, different genotypes adopted various phenotypic adjustment strategies with sp5 developing higher, flacca developing lower and AC maintaining SLA. Drought stress induced the significant accumulation of ABA in leaf, especially in sp5, but relatively lower in flacca . However, compared to AC and sp5, flacca accumulated large amounts of ethylene under drought, suggesting that in plants with ABA deficiency, ethylene may play a compensatory role in controlling stomatal closure during soil drying. Plants with different endogenous ABA concentrations adopted diverse strategies and showed various responses to cope with drought and e [CO 2 ]. These findings improve our understanding of plant performances to a future drier and CO 2 -enriched environment.