The physiology and control of re-greening in spathes of Zantedeschia : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Physiology at Massey University, Palmerston North, New Zealand
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Date
2011
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Massey University
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Abstract
Spathe re-greening is a primary determinant limiting postharvest quality of
Zantedeschia Spreng. as a cut flower, pot- or landscape-plant. A treatment that can be
utilised by growers to delay re-greening offers potential to improve the postharvest
quality and provide a marketing advantage. To achieve this, and develop an
understanding of the physiological mechanism of re-greening, this project
investigated the changes in colour, levels and types of pigment, and differentiation of
plastids in spathe tissue durng re-greening; and how this process was controlled by
various factors including fructification, light and various plant hormones (e.g.
cytokinin and gibberellin).
In the hybrid ‘Best Gold’, spathe re-greening was initiated within three days
after horticultural harvest-maturity and, within two weeks the whole abaxial surface
of the spathe had re-greened. During this period, the adaxial surface did not re-green
and remained yellow in colour. The change in colour of the abaxial surface primarily
resulted from the accumulation of chlorophyll within the subepidermal layers, as
reflected by a strong correlation between the colour coordinate hue angle (Hº) and
total chlorophyll content in that surface (r = 0.98). Monitoring Hº can therefore, be
used to evaluate the degree of re-greening for ‘Best Gold’ without chlorophyll
analysis. The content of carotenoid (in particular lutein which was predominant) was
comparatively steady during re-greening. From an ultrastructural perspective, spathe
re-greening was characterized by redifferentiation of chloroplasts from chromoplasts,
as compared with de novo synthesis of chloroplasts from proplastids. The
redifferentiation of chloroplasts involved thylakoid reformation through multiple
mechanisms. In addition to de novo synthesis of thylakoid by invaginations of the
inner-envelope membrane, it is likely that the thylakoids were either derived from
primary thylakoids or plastoglobuli present in mature chromoplasts.
The occurrence of re-greening in the spathe of both Zantedeschia aethiopica
and ‘Best Gold’ following the removal of the spadix prior to pollination, contradicted
the hypothesis that re-greening was induced by fructification (Pais and Neves, 1982-
1983). Further to this, the occurrence of re-greening in the spathe of ‘Best Gold’ with
a spadix naturally devoid of female flowers, and the re-greening of pigmented leaves
devoid of any true flower parts, also contradicted this hypothesis. The current findings
therefore, indicate that fructification is not necessarily a prerequisite for induction of
re-greening.
In absence of light, no chlorophyll accumulated in spathe tissue of ‘Best Gold’,
but the initial redifferentiation of chloroplasts from chromoplasts, as characterized by
the formation of double-membrane lamella, was noted. Without light however,
redifferentiation of chloroplasts was not completed. These suggest spathe re-greening
requires light for the process to complete, but the onset of re-greening can be induced
in darkness. The application of 6-benzylaminopurine (BAP) stimulated re-greening in
spathe tissue by enhancing accumulation of carotenoid and chlorophyll, and also
stacking of grana. But the response to BAP was dependent on the presence/absence of
light, the stage of re-greening, and which surface, i.e. abaxial or adaxial. In contrast,
the application of gibberellin (GA3) retarded formation of double-membrane lamella,
and thus delayed the onset of re-greening. Hence, a synergistic effect of BAP and GA3
in delaying the onset of re-greening was likely to be a result of co-regulation between
BAP-stimulated accumulation of carotenoid and GA3-stimulated retardation of
chloroplast redifferentiation.
By integrating both light and hormonal factors, several methods were tested on
the actual horticultural commodity, i.e. flowers (peduncle, spathe and spadix) of ‘Best
Gold’, so as to evaluate their efficacy in delaying re-greening. Pulsing flowers in
darkness at 5 ºC for 24-h in a solution containing both GA3 and BAP, was the most
effective treatment in postponing re-greening, resulting in a seven-day delay in regreening
of the spathe.
Description
Content removed due to copyright restrictions: Chen, J., Funnell, K.A., & Woolley, D.J.(2009). Abaxial and adaxial surfaces of spathe tissue
of Zantedeschia differ in their pattern of re-greening. Acta Horticulturae. 183, 217-224.
Keywords
Calla lilies, Zantedeschia, Postharvest physiology, Spathes, Re-greening