Mechanisms underlying the long-term survival of the monocot Dracaena marginata under drought conditions

Abstract

Efficient water management is essential for the survival of vascular plants under drought stress. While interrelations among drought stress, plant anatomy and physiological functions have been described in woody dicots, similar research is very limited for non-palm arborescent and shrubby monocots despite their generally high drought tolerance. In this study, potted transplants of Dracaena marginata Lam. in primary growth stage were exposed to several short- and long-term drought periods. Continuous measurements of sap flow and stem diameter, the evaluation of capacitance and leaf conductance, the quantification of non-structural carbohydrates (NSC), and organ-specific anatomical analyses were performed to reveal the mechanisms promoting plant resistance to limited soil moisture. The plants showed sensitive stomata regulation in the face of drying soil, but only intermediate resistance to water loss through cuticular transpiration. The water losses were compensated by water release from stem characterized by densely interconnected, parenchyma-rich ground tissue and considerable hydraulic capacitance. Our results suggest that the high concentration of osmotically active NSC in aboveground organs combined with the production of root pressures supported water uptake and the restoration of depleted reserves after watering. The described anatomical features and physiological mechanisms impart D. marginata with high resistance to irregular watering and long-term water scarcity. These findings should help to improve predictions with respect to the impacts of droughts on this plant group.

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“…from 1 to 13 µm and fiber bundles are mostly hypodermal [43,84,85] (Figure 3b). The drought resistance of these species could also be very high, despite the more mesomorphic appearance, as a recent study on young transplants of mesophytic D. marginata confirmed [86]. The xeromorphic species have more deeply sunken stomata (D. ombet, D. serrulata, and D. cinnabari) (Figure 3c), which are distributed irregularly or parallel to the leaf axis regularly over the entire area [13,43,84].…”

“…Dracaena leaves are mostly amphistomatic with stomata on both leaf sides [43,84] (Figure 3a,b), but hypostomatic leaves with stomata on only the adaxial side were also observed (e.g., D. ellenbeckiana) [87]. The stomatal density varies along the leaf axis as well as between midrib and leaf margins [84,86] and, in general, the stomatal density increases towards the more xeromorphic appearance (approx. 30-90 stoma per mm 2 ) [84,86].…”

“…The stomatal density varies along the leaf axis as well as between midrib and leaf margins [84,86] and, in general, the stomatal density increases towards the more xeromorphic appearance (approx. 30-90 stoma per mm 2 ) [84,86]. Higher stomatal density was mostly observed on the abaxial leaf side [87].…”

“…Vascular bundles are collateral and they are surrounded by a well-developed sclerenchymatous sheath [43,84] ( Figure 3a,b). Calcium oxalate crystals in the form of raphides are quite abundant in leaves [43,86].…”

“…There are no special secondary radial tissues providing radial symplastic transport as ray parenchyma in coniferous or dicotyledonous trees in arborescent monocots with secondary growth [100,101]. However, the parenchyma cells in the secondary ground tissue are produced in regular radial files (in contrast to the primary ground tissue that shows no such pattern) [72] and those ground parenchyma cells are typically densely interconnected by simple pits that are present in their cell walls [86]. Therefore, it can be anticipated that the ground parenchyma might serve as an extra-fascicular symplastic transport pathway [84,99].…”