Morphological, Physiological and Ultrastructural Changes in Flowers Explain the Spatio-Temporal Emission of Scent Volatiles in Polianthes tuberosa L.

Abstract

Tuberose or Polianthes tuberosa L. is a horticultural crop of tropical origin, widely cultivated for its pleasant and intense floral fragrance in the evening. Here an investigation was made into the physiological and cell biological aspects of floral scent biosynthesis, tissue localization and emission that have not previously been examined. Volatiles collected from floral headspace were analyzed by gas chromatography-mass spectrometry (GC-MS) for identification of individual compounds and elucidation of emission patterns. Transcript accumulation and the amount of active enzyme were measured to understand the enzymatic route of scent volatile biosynthesis. Localization of scent volatiles was investigated by histochemical and ultrastructural studies. Scent emission was found to be rhythmic and nocturnal under normal day-night influence, peaking at night. Enhanced enzyme activities and transcript accumulation were recorded just prior to maximum emission. Through scanning electron microscopy (SEM) analysis, the presence of a large number of floral stomata on the adaxial surface of the tepal was revealed which might have bearing on tissue-specific emission. Guard cells of stomata responded significantly to histochemical tests, which also indicated that epidermal tissues are mostly involved in scent emission. High metabolic activity was found in epidermal layers during anthesis as shown by transmission electron microscopy (TEM) analysis. Further, new insight into the localization of scent compounds, the plausible tissue involved in their release along with the preceding ultrastructural changes at the cellular levels is presented. Finally, ultrastructural analysis of the tepal surface has been able to fill a major gap in knowledge of stomatal involvement during scent emission.