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

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.

Methods for characterizing plant fibers.

The effectiveness of different microscopy techniques for measuring the dimensions of ultimate fibers from harakeke (Phormium tenax, New Zealand flax) was investigated using a factorial experimental design. Constant variables were geographical location, location of specimens along the leaf, season (winter), individual plant, a fourth leaf from a north-facing fan, age of plant, and cultivars (two). Experimental variables were microscopy techniques and measurement axis. Measurements of width and length of harakeke ultimate fibers depended on the microscopic preparation/technique used as well as the cultivar examined. The best methods were (i) transverse sections of leaf specimens 4 microm thick, embedded in Paraplast and observed using light microscopy, and (ii) nonfixed ultimate fibers observed using scanning electron microscopy.