Nectary photosynthesis contributes to the production of mānuka (Leptospermum scoparium) floral nectar

Michael J. Clearwater, Stevie T. Noe, Merilyn Manley-Harris, Georgia Leigh Truman, Stephen Gardyne, Jessica Murray, Sylvester A. Obeng-Darko, Sarah J. Richardson

Research output: Contribution to journalArticlepeer-review

Abstract

Current models of floral nectar production do not include a contribution from photosynthesis by green nectary tissue, even though many species have green nectaries. Mānuka (Leptospermum scoparium) floral nectaries are green, and in addition to sugars, their nectar contains dihydroxyacetone (DHA), the precursor of the antimicrobial agent in the honey. We investigated causes of variation in mānuka floral nectar production, particularly the effect of light incident on the nectary. Flower gas exchange, chlorophyll fluorescence, and the effects on nectar of age, temperature, light, sucrose, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), pyridoxal phosphate, and 13CO2, were measured for attached and excised flowers. Flower age affected all nectar traits, whilst temperature affected total nectar sugar only. Increased light reduced floral CO2 efflux, increased nectar sugar production, and affected the ratio of DHA to other nectar sugars. DCMU, an inhibitor of photosystem II, reduced nectar sugar production. Pyridoxal phosphate, an inhibitor of the chloroplast envelope triose phosphate transporter, reduced nectar DHA content. Incubation of excised flowers with 13CO2 in the light resulted in enrichment of nectar sugars, including DHA. Photosynthesis within green nectaries contributes to nectar sugars and influences nectar composition. Mānuka nectar DHA arises from pools of triose phosphate that are modulated by nectary photosynthesis.

Original languageEnglish
Pages (from-to)1703-1717
Number of pages15
JournalNew Phytologist
Volume232
Issue number4
DOIs
Publication statusPublished - Nov 2021

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