Abstract
Defoliants can increase machine harvest efficiency of cotton (Gossypium hirusutum L.), prevent lodging and reduce the time from defoliation to harvest. Coronatine (COR) is a chlorosis-inducing non-host-specific phytotoxin that induces leaf and/or fruit abscission in some crops. The present study investigates how COR might induce cotton leaf abscission by modulating genes involved in cell wall hydrolases and ACC (ethylene precursor) in various cotton tissues. The effects of COR on cotton boll ripening, seedcotton yield, and seed development were also studied. After 14 d of treatment with COR, cells within the leaf abscission zone (AZ) showed marked differentiation. Elevated transcripts of GhCEL1, GhPG and GhACS were observed in the AZs treated with COR and Thidiazuron (TDZ). The relative expression of GhCEL1 and GhACS in TDZ treated plants was approximately twice that in plants treated with COR for 12 h. However, only GhACS expression increased in leaf blade and petiole. There was a continuous increase in the activity of hydrolytic enzymes such as cellulase (CEL) and polygalacturonase (PG), and ACC accumulation in AZs following COR and TDZ treatments, but there was greater increase in ACC activity of COR treated boll crust, indicating that COR had greater ripening effect than TDZ. Coronatine significantly enhanced boll opening without affecting boll weight, lint percentage and seed quality. Therefore, COR can be a potential cotton defoliant with different physiological mechanism of action from the currently used TDZ.
Highlights
Cotton is an important commercial crop worldwide, and serves as a significant source of fiber, feed, foodstuff, oil and biofuel [1]
abscission zone (AZ) of plants treated with COR and their control were examined under scanning microscopy in order to elucidate the anatomical alterations in AZs (Fig. 2)
We demonstrated that the phytotoxin, coronatine induced leaf abscission during cotton defoliation
Summary
Cotton is an important commercial crop worldwide, and serves as a significant source of fiber, feed, foodstuff, oil and biofuel [1]. The ultimate goal of defoliants is to facilitate mechanical harvest, reduce trash and protect fiber and seed quality from weathering and staining by allowing earlier harvest [4]. Another benefit is the reduced moisture content in the raw fibers and seed which is essential for storage of seedcotton. Dimethipin is considered a contact-type defoliant, whereas thidiazuron has growth-regulator properties and moves through the plant [7]. Thidiazuron increases the concentration of ethylene relative to auxin in leaf petioles and results in the activation of the leaf abscission layer [8,9] These types of defoliants induce drastic leaf abscission which inhibits timely transport of nutrients from leaves to cotton bolls. An abscission chemical with improved defoliation and boll opening properties is needed for cotton harvest practices
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