Abstract
Plants are in danger of embolism formation in xylem vessels when the balance between water transport capacity and transpirational demand is compromised. To maintain this delicate balance, plants must regulate the rate of transpiration and, if necessary, restore water transport in embolized vessels. Abscisic acid (ABA) is the dominant long-distance signal responsible for plant response to stress, and it is possible that it plays a role in the embolism/refilling cycle. To test this idea, a temporal analysis of embolism and refilling dynamics, transpiration rate and starch content was performed on ABA-deficient mutant tomato plants. ABA-deficient mutants were more vulnerable to embolism formation than wild-type plants, and application of exogenous ABA had no effect on vulnerability. However, mutant plants treated with exogenous ABA had lower stomatal conductance and reduced starch content in the xylem parenchyma cells. The lower starch content could have an indirect effect on the plant’s refilling activity. The results confirm that plants with high starch content (moderately stressed mutant plants) were more likely to recover from loss of water transport capacity than plants with low starch content (mutant plants with application of exogenous ABA) or plants experiencing severe water stress. This study demonstrates that ABA most likely does not play any direct role in embolism refilling, but through the modulation of carbohydrate content, it could influence the plant’s capacity for refilling.
Highlights
Plants subject to water stress are susceptible to cavitation and the formation of embolism in xylem conduits [1]
Concentration levels were similar in irrigated not and sit mutant lines and significantly lower than well-watered wild-type plants. This initial difference was later magnified during increasing water stress, while in both mutant lines, the stress treatment had no effect on Abscisic acid (ABA)
During recovery from stress, the level of ABA dropped in wt plants, while
Summary
Plants subject to water stress are susceptible to cavitation and the formation of embolism in xylem conduits [1]. The presence of embolism results in the loss of xylem capacity to transport water to meet the transpirational demand [2,3] and could lead to desiccation or death of photosynthetic tissue in the event of runaway cavitation [4]. Rapid changes in water demand due to changing humidity, light exposure and temperature require mechanisms that respond in much shorter time scales These short-term responses rely on stomatal movement [7] and on the plant’s ability to restore water transport in embolized conduits [8,9,10,11]. The role of embolism removal and restoration of the xylem transport capacity is much less understood, the process might be partially affected by the same stress related factors, enforcing a coordinated plant behavior [17]
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