Leaf gas exchange and water relations of the woody desiccation-tolerant Paraboea rufescens during dehydration and rehydration

Abstract

Desiccation-tolerant (DT) plants can withstand dehydration to less than 0.1 g H₂O g^-1 dry weight. The mechanism for whole-plant recovery from severe dehydration is still not clear, especially for woody DT plants. In the present study, we evaluated the desiccation tolerance and mechanism of recovery for a potentially new woody resurrection plant Paraboea rufescens (Gesneriaceae). We monitored the leaf water status, leaf gas exchange, chlorophyll fluorescence and root pressure of potted P. rufescens during dehydration and rehydration, and we investigated the water content and chlorophyll fluorescence of P. rufescens leaves in the field during the dry season. After re-watering from a severely dehydrated state, leaf maximum quantum yield of photosystem II of P. rufescens quickly recovered to well-watered levels. Leaf water status and leaf hydraulic conductance quickly recovered to well-watered levels after re-watering, while leaf gas exchange traits also trended to recovery, but at a slower rate. The maximum root pressure in rehydrated P. rufescens was more than twice in well-watered plants. Our study identified P. rufescens as a new DT woody plant. The whole-plant recovery of P. rufescens from extreme dehydration is potentially associated with an increase of root pressure after rehydration. These findings provide insights into the mechanisms of recovery of DT plants from dehydration.

Keywords: Desiccation tolerance; Gesneriaceae; Paraboea rufescens; leaf hydraulic conductance; rehydration; resurrection plant; root pressure.

Figure 1.

Photographs of well-watered and dehydrated Paraboea rufescens in the field. (A) A well-watered P. rufescens in the rainy season. (B) A dehydrated P. rufescens in the dry season. (C) A dehydrated P. rufescens with a long stem in the dry season.

Figure 2.

Leaf dark-adapted maximum quantum yield of photosynthetic system II (F_v/F_m) of re-watered and well-watered Paraboea rufescens. Means ± SE (n = 4–5) for leaves from well-watered plants (W), for leaves from severely dehydrated potted plants after re-watering for 3 (r3), 4 (r4) and 5 days (r5) and for rehydrated leaves collected from the field at the peak of the dry season (F, n = 9) are shown. Different letters above the bars indicate significant differences among means across treatments compared using Tukey’s honest significant difference test (P < 0.05).

Figure 3.

Changes in leaf water status, gas exchange and chlorophyll fluorescence in Paraboea rufescens during dehydration and re-watering. (A) leaf water content (LWC), (B) leaf water potential (Ψ_leaf), (C) leaf hydraulic conductance (K_leaf), (D) maximum stomatal conductance (g_s), (E) leaf area-based photosynthetic rate (A_a) and (F) quantum efficiency of photosynthetic system II (Φ_PSII). Values were means ± SE (n = 4–5) taken from well-watered individuals (W), after withholding water for 1–27 days (d1–d27) and after re-watering for 1–5 days (r1–r5). The LWC of leaves collected from the field at the peak of dry season is also given (‘F’ in panel A, n = 9). Different letters above the bars indicate significant differences among means across treatment compared using Tukey’s honest significant difference test (P < 0.05).

Figure 4.

Correlations in Paraboea rufescens between leaf water potential (Ψ_leaf) and stomatal conductance (g_s) (A), maximum area-based photosynthetic rate (A_a) (B), leaf hydraulic conductance (K_leaf) (C) and quantum efficiency of photosynthetic system II (Φ_PSII) (D). Data obtained during dehydration (open circles) and during re-watering (closed circles) are shown. Dashed lines indicate the leaf water potential at the turgor loss point (Ψ_tlp). Black lines show the trends in the combined data from both plant dehydration and re-watering. Data were fit using the generalized additive model.

Figure 5.

Dynamics of root pressure fluctuations in Paraboea rufescens in well-watered individuals (A) and in re-watered individuals recovering from severe dehydration (B), with photos of the four individuals examined during re-watering (C). Different coloured lines and symbols correspond to different individuals. The shaded areas in (A) and (B) indicate the hours of darkness from 19:00 to 7:00.