In Vivo Cell Wall Loosening by Hydroxyl Radicals during Cress Seed Germination and Elongation Growth    

Abstract

Loosening of cell walls is an important developmental process in key stages of the plant life cycle, including seed germination, elongation growth, and fruit ripening. Here, we report direct in vivo evidence for hydroxyl radical ( × OH)-mediated cell wall loosening during plant seed germination and seedling growth. We used electron paramagnetic resonance spectroscopy to show that × OH is generated in the cell wall during radicle elongation and weakening of the endosperm of cress (Lepidium sativum; Brassicaceae) seeds. Endosperm weakening precedes radicle emergence, as demonstrated by direct biomechanical measurements. By 3 H fingerprinting, we showed that wall polysaccharides are oxidized in vivo by the developmentally regulated action of apoplastic × OH in radicles and endosperm caps: the production and action of × OH increased during endosperm weakening and radicle elongation and were inhibited by the germination-inhibiting hormone abscisic acid. Both effects were reversed by gibberellin. Distinct and tissue-specific target sites of × OH attack on polysaccharides were evident. In vivo × OH attack on cell wall polysaccharides were evident not only in germinating seeds but also in elongating maize (Zea mays; Poaceae) seedling coleoptiles. We conclude that plant cell wall loosening by × OH is a controlled action of this type of reactive oxygen species.

Carboxymethylcellulase Activity in Lettuce Seeds Prior to Germination

“…The lettuce seed endosperm when sown in isocyanuric acid is capable of resisting the expansion force of the embryo resulting in embryo expansion without endosperm rupture ("buckling") and protrusion at the cotyledon end or along the side ("atypical germination") [23]. Atypical germination was also reported with cress seeds [24].…”

Role of Reactive Oxygen Species during Cell Expansion in Leaves

“…Studies on leaf expansion in maize under saline conditions revealed a decreased O 2 2 -derived _ OH production in the apoplast and a consequent reduction in leaf growth (Rodríguez et al, 2004). Interestingly, it was found that _ OH promotes cell elongation by loosening the cell wall through oxidative cleavage of polymers like xyloglucan and pectin (Fry, 1998;Müller et al, 2009). In the presence of transition metals, the Haber-Weiss reaction can convert H 2 O 2 and O 2 2 anions to _ OH, a reaction that can be performed both nonenzymatically as well as enzymatically (Chen and Schopfer, 1999).…”

Intracellular Redox Compartmentation and ROS-Related Communication in Regulation and Signaling

“…However, many basic processes involved in cell wall growth and dynamics require a highly oxidizing environment. Unlike the cell interior, the wall requires the generation of strong oxidants such as the hydroxyl radical (Müller et al, 2009). Consequently, the apoplast has evolved a relatively low capacity for antioxidant accumulation, together with enzymes that actively remove these compounds (Pignocchi and Foyer, 2003;Ohkama-Ohtsu et al, 2007;Parsons and Fry, 2012).…”