Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

Abstract

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO 2 concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F v /F m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.Additional key words: chlorophyll; drought; intercellular CO 2 concentration; leaf water potential; non-photochemical quenching; photochemical activity; rehydration; stomatal conductance to water vapour; transpiration rate. ---The leaf water status and carbon uptake is under stomata control and stomata closure is one of the earliest responses to drought, resulting in protection of the plants against harmful dehydration but also inevitably results in reduction of CO 2 uptake for photosynthesis. The stomata control is important only under mild stress (Cornic 2000). However, metabolic inhibition of photosynthesis also takes place at mild water stress (Tezara et al. 1999) and it becomes more important as the water stress intensifies. Most of the studies in this area were done on mature leaves and the few available data comparing the effects of water stress on mature and young leaves indicate that the photosynthetic responses to water stress are strongly dependent on leaf age (David et al. 1998). In addition, there are indications that water stress accelerates leaf senescence (Olsson 1995).The accumulation of osmolyte compounds in the cells as a result of water stress is often associated with a possible mechanism to tolerate the harmful effect of water shortage. The contribution of sugars as an osmotic solute in expanded and partly expanded sunflower leaves was studied by Jones and Turner (1980). They found that contents of sugars did not change in fully expanded leaves. In opposition, the contents of soluble sugars in partly expanded leaves were reduced. In addition to sugars, some plants also accumulate other low molecular mass compounds, such as proline (Gzik 1996, Bajji et al. 2001. These osmolyte accumulations in plant cells might contribute, via lowering the cell osmotic potential, to maintaining several physiological processes, such as photosynthesis, stomatal conductance, and leaf expansion even under stressed conditions. The present experiment was designed to study the responses of photosynthesis to water stress in fully expanded and expanding leaves of sunflower plants. Additionally, the change in proline content and the ability of plants to recover from the water stres...

Differential responses between mature and young leaves of sunflower plants to oxidative stress caused by water deficit

“…The accumulation of osmolyte compounds such as proline in the cells as a result of water stress is often associated with a possible mechanism to tolerate the harmful effect of water shortage (CLIFFORD et al, 1998). In sunflower, the young stressed leaves synthesized nearly seven times more proline than non-stressed leaves while the mature stressed leaves synthetized it only four times more (CECHIN et al, 2006). This may explain the lower leaf young stressed leaves found in this study.…”

Physiological characteristics, antioxidant enzyme activities, and gene expression in 2 spring canola (Brassica napus L.) cultivars under drought stress conditions

“…The highest proline was observed under high stress conditions (25AW) in RGS003 (142.63 nmol/g fresh weight), and the lowest proline was observed in the RGS003 cultivar under normal conditions (23.68 nmol/g fresh weight) (Figure 3). Cechin et al (2006) investigated the response of photosynthesis and proline under stress in leaves of the safflower oil plant and showed that drought stress increased proline accumulation in young leaves. Din et al (2011) found that metabolic factors such as free proline content in leaves increased significantly under severe drought stress at both the reproductive and the productive stage.…”

Nitric oxide reduces oxidative damage induced by water stress in sunflower plants

“…After four days of stress imposition, leaf and shoot dry weight and RWC were reduced about 23%, 22% and 13%, respectively but stem dry weight accumulation was not affected (Table 1). The observed reduction in leaves dry weight is a result of high sensitivity of young leaves to changes in water supply (Cechin et al, 2006) since cell division and elongation are influenced by leaf water status or cell turgor (Heckenberger et al, 1998). Applications of SNP in wheat seedlings has been found to confer water deficit tolerance by maintaining more water than the well watered plants (García-Mata & Lamattina, 2001).…”

“…Proline works as both an osmoprotectant and as a redox-buffering agent possessing antioxidant property under conditions of stress (KaviKishor & Sreenivasulu, 2014). Accumulation of proline under drought stress was found in several plants, particularly in young leaves (Cechin et al, 2006). Furthermore, foliar applied proline ameliorated the adverse effects of water stress on growth and photosynthetic capacity of two maize cultivars (Ali et al, 2007).…”