Title of Work

The role of alanine synthesis and nitrate‐induced nitric oxide production during hypoxia stress in Cucurbita pepo nectaries

Document Type

Article

Publication/Presentation Date

October 2020

DOI

doi.org/10.1111/tpj.15055

Abstract

Floral nectar is a sugary solution produced by nectaries to attract and reward pollinators. Nectar metabolites, such as sugars, are synthesized withinthe nectary during secretion from both pre‐stored and direct phloem‐derived precursors. In addition to sugars, nectars contain nitrogenous compounds such as amino acids, howeverlittle is known about the role(s) of N‐compounds in nectary function. In this study, we investigated nitrogen (N) metabolism in Cucurbita pepo (squash) floral nectaries in order to understand how various N‐containing compounds are produced and determine the role of N‐metabolism in nectar secretion. The expression and activity of key enzymes involved in primary N‐assimilation, including nitrate reductase (NR) and alanine aminotransferase (AlaAT),were induced during secretion in C. pepo nectaries. Alanine accumulated to ~35% of total amino acids in nectaries and nectar during peak secretion; however, alteration of vascular nitrate supply had no impact on Ala accumulation during secretion, suggesting nectar(y) amino acids are produced by precursors other than nitrate. In addition, nitric oxide (NO) is produced from nitrate and nitrite, at leastpartially by NR, in nectaries and nectar. Hypoxia‐related processes are induced in nectaries during secretion, including lactic acid and ethanolic fermentation.Finally, treatments that alternitrate supplyimpact levels of hypoxic metabolites, nectar volume, andnectar sugar composition. The induction of N‐metabolism in C. pepo nectariesthus plays an importantrole in the synthesis and secretion of nectar sugar.

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