Abstract
In germinating seeds under unfavorable environmental conditions, the mobilization of stores in the cotyledons is delayed, which may result in a different modulation of carbohydrates balance and a decrease in seedling vigor. Tall fescue (Festuca arundinacea Schreb.) caryopses grown at 4°C in the dark for an extended period in complete absence of nutrients, showed an unexpected ability to survive. Seedlings grown at 4°C for 210 days were morphologically identical to seedlings grown at 23°C for 21 days. After 400 days, seedlings grown at 4°C were able to differentiate plastids to chloroplast in just few days once transferred to the light and 23°C. Tall fescue exposed to prolonged period at 4°C showed marked anatomical changes: cell wall thickening, undifferentiated plastids, more root hairs and less xylem lignification. Physiological modifications were also observed, in particular related to sugar content, GA and ABA levels and amylolytic enzymes pattern. The phytohormones profiles exhibited at 4 and 23°C were comparable when normalized to the respective physiological states. Both the onset and the completion of germination were linked to GA and ABA levels, as well as to the ratio between these two hormones. All plants showed a sharp decline in carbohydrate content, with a consequent onset of gradual sugar starvation. This explained the slowed then full arrest in growth under both treatment regimes. The analysis of amylolytic activity showed that Ca2+ played a central role in the stabilization of several isoforms. Overall, convergence of starvation and hormone signals meet in crosstalk to regulate germination, growth and development in tall fescue.
Highlights
In higher plants, sugars function as metabolic energy storage and structural cellular components, but they serve as regulators of plant growth and development
Seedlings grown under control conditions showed differences in the elongation of organs at 21 DAS, while coleoptile showed a high increase in comparison to 12 DAS, root length was maintained
Since we previously found that stable amylase isoforms were induced by prolonged exposure to cold stress (210 and 400 DAS) (Fig 7), we examined whether the stabilization factors found in the tall fescue extracts would be able to stabilize the amylolytic activity in other plant species
Summary
Sugars function as metabolic energy storage and structural cellular components, but they serve as regulators of plant growth and development. Plants are largely considered carbon autotrophs, they can be viewed as carbon heterotrophs during certain stages of their life cycle, e.g. senescence, postharvest period or seed germination [1]. Inefficient breakdown of carbohydrates may quickly drain the carbohydrate stores in sink tissues during night [2], as well as when plants may be exposed to biotic or abiotic stresses that affect photosynthetic efficiency in source tissues [3]. Physiological and biochemical changes aimed at sustaining respiration and metabolic processes, due to a complex sugar-sensing network. Sugar starvation generally triggers the following sequential cellular events: (a) arrest in cell growth, (b) rapid consumption of cellular carbohydrate and decrease in respiration rate, (c) degradation of lipids and proteins, (d) increase in accumulation of phosphate, phosphorylcholine and free amino acids, and (e) decline in glycolytic enzymatic activities [1]
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