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Tobacco floral nectaries undergo changes in form and function. As nectaries change from green to orange, a new pigment is expressed. Analysis demonstrated that it is β-carotene. Plastids undergo dramatic changes. Early in nectary development, they divide and by stage 9 (S9) they are engorged with starch. About S9, nectaries shift from quiescent anabolism to active catabolism resulting in starch breakdown and production of nectar sugars. Starch is replaced by osmiophilic bodies, which contain needle-like carotenoid crystals. Between S9 and S12, amyloplasts are converted to chromoplasts. Changes in carotenoids and ascorbate were assayed and are expressed at low levels early in development; however, following S9 metabolic shift, syntheses of β-carotene and ascorbate greatly increase in advance of expression of nectar redox cycle. Transcript analysis for carotenoid and ascorbate biosynthetic pathways showed that these genes are significantly expressed at S6, prior to the S9 metabolic shift. Thus, formation of antioxidants β-carotene and ascorbate after the metabolic shift is independent of transcriptional regulation. We propose that biosynthesis of these antioxidants is governed by availability of substrate molecules that arise from starch breakdown. These processes and events may be amenable to molecular manipulation to provide a better system for insect attraction, cross pollination, and hybridization.

Chamelaucium uncinatum Schauer. (Geraldton wax) is well known as a garden and cut-flower species in Western Australia. The location of pigmented cells and the shape of the epidermal cells that interact with incident light can affect flower colour. This study examined the location of pigments within petals of three C. uncinatum cultivars, 'Purple Pride', 'CWA Pink' and 'Alba', which represent the range of colours found in this species. The white cultivar ('Alba') lacked coloured pigments in the petals while the pink ('CWA Pink') and purple ('Purple Pride') cultivars had pigmented vacuoles in petal epidermal and mesophyll cells. A waxy coating was present on petal epidermal cells of all cultivars and cells of the adaxial epidermis were found to be conical. Patterns in petals of 'CWA Pink' and 'Purple Pride' were due to cultivar-specific location of pigments.

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