Vegetative desiccation tolerance in Eragrostiella brachyphylla: biochemical and physiological responses

Abstract

Eragrostiella brachyphylla is an angiosperm desiccation-tolerant resurrection plant, which can survive during desiccation in the air-dry state and recover completely on availability of water. The present study was conducted to understand the vegetative desiccation tolerance of Eragrostiella brachyphylla by evaluating its ability to recover the physiological, biochemical and morphological functions post desiccation. In order to understand the responses of Eragrostiella brachyphylla to desiccation and subsequent rehydration experiments were conducted in the hydrated state (HS), desiccated state (DS) and rehydrated state (RS). Scanning electron microscopy revealed significant changes between the three stages in the internal ultra-structures of leaves and stems. Compared to the other states, photosynthetic parameters such as chlorophyll a, chlorophyll b, total chlorophylland total carotenoid contents decreased significantly in the desiccated state. Superoxide radical (O2^•-) content also increased, resulting in an oxidative burst during desiccation. Consequently, antioxidant enzymes such as catalase (CAT) superoxide dismutase (SOD) peroxidase (APX) and glutathione reductase (GR) activities were found to be significantly elevated in the desiccated state to avoid oxidative damage. Increased malondialdehyde (MDA) content and relative electrolyte leakage (REL) during desiccation provide evidence for membrane damage and loss of cell-wall integrity. During desiccation, the contents of osmolytes represented by sucrose and proline were found to increase to maintain cell structure integrity. After rehydration, all physiological, biochemical and morphological properties remain unchanged or slightly changed when compared to the hydrated state. Hence, we believe that these unique adaptations contribute to the remarkable desiccation-tolerance property of this plant.

Keywords: Antioxidant enzymes; Desiccation tolerance; Photosynthesis; Plant biology; Proline; REL; RWC; Ultrastructure.

Figure 1

Images of E. brachyphyllacaptured atDeverayanadurga Reserve Forest (Coordinates-13.3737° N, 77.2075° E), Tumakuru district of Karnataka state, India (A & B hydrated. C & D desiccated).

Figure 2

E. brachyphylla resurrection grass, a. Well-watered (relative water content:100 %). b. Desiccated (relative water content:8 %) after two days of withholding water. c. Rehydrated for 12 h post-hydration (relative water content:92%). The heat map below represents the rehydration potential (ability to rehydrate) of the resurrection grass E. brachyphylla. HS, Well-watered (relative water content: 100%). DS, Desiccated (relative water content 8 %) after two days of withholding water. RS, Condition 24 h post-hydration (relative water content:92%). with three replicates (n = 3).

Figure 3

Scanning electron microscopic images of hydrated (A& B stem, C leaf), desiccated (D & E stem, F leaf), and rehydrated (G & H stem, I leaf) at different magnifications (A, D and G 200x; B, E and H 500x; C, F and I 1000x).

Figure 4

Pigment composition in E. brachyphylla, (a) Total chlorophyll, (b) CO₂ exchange rate [CER], (c) Anthocyanin and (d) Carotenoids estimated during Hydrated (HS), Desiccated (DS) and rehydrated (RS) states. Data represent the means ± SE of three separate experiments. ∗P ≤ 0.01, ∗∗P ≤ 0.001.

Figure 5

Activities of antioxidant enzymes in E. brachyphylla. (a) Superoxide dismutase (SOD); (b) Catalase (CAT), (c) Peroxidase (POD) and (d) Glutathione reductase (GR) in Hydrated (HS), Desiccated (DS) and rehydrated (RS) states. Data represent the means ± SE of three biological replicates. ∗P ≤ 0.01, ∗∗P ≤ 0.001.

Figure 6

Proline accumulation (a), REL (b), Changes in the levels of MDA (c) and Quantity of superoxide radical (d) in Hydrated (HS), Desiccated (DS) and rehydrated (RS) states of E. brachyphylla. Data represent the means ± SE of three separate experiments. ∗P ≤ 0.01, ∗∗P ≤ 0.001. ∗∗∗P ≤ 0.0001.

Figure 7

Changes in the level of sucrose (a) and of starch (b) in HS, DS and RS of E. brachyphylla. Data represent the means ± SE of three separate experiments. ∗P ≤ 0.01, ∗∗P ≤ 0.001. ∗∗∗P ≤ 0.0001.