Encuesta realizada a clientes de la Compañía Ciudad Rodrigo C.A.

Re-greening has been reported to occur in various organs of plants for a number of species. Re-greening of floral organs (e.g. petal, sepal, or bract) has been shown in Phalaenopsis Blume species (Tran et al., 1995), Helleborus niger L.

(Salopek-Sondi et al., 2002), Nuphar luteum L. (Gronegress, 1974), Orontium

aquaticum L. (Casadoro et al., 1982), Heliconia aurantiaca L. and Spathiphyllum wallisii Regel. (Weidner et al., 1985). Similar to the spathes of Zantedeschia, these

floral organs of other species undergo the same characteristic colour changes during flower development. These organs are usually green when they are very young, develop full colour during anthesis, and gradually re-green again after pollination and during subsequent fruit formation.

The re-greening extends the longevity of the floral organs and, in doing so, potentially ensures the successful development and maturation of seeds (Herrera, 2005; Salopek-Sondi et al., 2000). Moreover, this colour change also provides signals to pollinators that the flowers are no longer fertile, which in turn increases the efficiency of pollination for other flowers. These floral organs therefore, fulfil two roles:

 functioning as an attractant to pollinators during anthesis;

 as a potential source of energy for the developing seeds and fruits during re-greening.

In other plant species the transition between these two roles of the floral organs has been associated with the occurrence of fructification (Salopek-Sondi et al., 2000; Tran et al., 1995). While discussed further in Sections 1.4 and 1.5, the precise biochemical and molecular signals linking fructification and re-greening, remain largely unknown. For the purposes of providing a starting point for the research into spathe re-greening

of Zantedeschia presented in this thesis, it was assumed that what was known about

re-greening occurring in floral organs of other plant species was likely to be most influential.

In some species a yellowing leaf or cotyledon can be induced to re-green before the point where the tissue commits to senescence (van Doorn, 2005). This kind of re-greening has been examined in Nicotiana rustica L. (Zavaleta-Mancera et al.,

1999b), Linum usitatissimum L. (Greening et al., 1982), Glycine max (L.) Merr.

(Skadsen and Cherry, 1983) and Vicia faba L. (Dyer and Osborne, 1971). In these

plants, when the lower leaves or cotyledons turn yellow, they can be induced to re- green by the removal of all the younger leaves or by spraying the leaf or cotyledon with ammonium nitrate. This indicates that the yellowing resulted in part from internal competition for nitrogen, and was somehow reversible. In addition, this re- greening could only be induced when the roots were attached or when cytokinin was applied to the detached yellowing leaf or cotyledon. Since root tips were proposed as one of the sites for cytokinin synthesis, the cytokinin originating from the roots was suggested to be a trigger for the re-greening in the yellowing leaf or cotyledon after the removal of younger leaves (Colbert and Beever, 1981). As discussed further in Sections 1.4 and 1.5, re-greening in yellowing leaves or cotyledons has been extensively studied due to its connection with the process of leaf senescence. At the outset of the research presented in this thesis, it was unclear if re-greening in leaves, cotyledons and floral organs, e.g., spathe of Zantedeschia, share a similar biochemical

and molecular mechanism. But it was believed that the current knowledge of re- greening in leaves or cotyledons would provide some insight for research into spathe re-greening in Zantedeschia.

Re-greening has been observed on the peel of ripe fruits of Citrus sinensis (L.)

Osbeck when left on the tree till the following spring or summer (Huff, 1983; Thomson et al., 1967), and also on the harvested fruits of Cucumis sativus L.(Prebeg

et al., 2008), Citrus grandis Merr. (Saks et al., 1988) and Cucurbita pepo L. (Devide

and Ljubesic, 1974), when exposed to light. The skin of these fruit is green at an immature stage, turns yellow when mature and, gradually develops a green colour again after maturity. Re-greening in fruits like these has not been extensively studied and, to date, the evolutionary advantage that might be gained from re-greening remains unclear.

In summary, re-greening of plant tissue is a unique but not rare process occurring naturally during plant development. It is present naturally or artificially in various organs of plants including leaves, cotyledons, floral organs and fruits. Despite its occurrence in different parts of plants, re-greening of these tissue shares many similarities from the perspective of the physiological mechanism including regaining of green colouration, accumulation of chlorophyll, reformation of chloroplasts (discussed further in Section 1.4.4), and potentially serving as an alternative source of photosynthate (Prebeg et al., 2008; Salopek-Sondi et al., 2000; Zavaleta-Mancera et al., 1999b). However, re-greening in these various plant organs might differ in the mechanism of how this process is induced and proceeds. For example, re-greening in sepals of H. niger was believed to be induced (at least in part) by fructification

(Salopek-Sondi et al., 2000; Tarkowski et al., 2006). Re-greening in peel of fruits in C.

sinensis on the other hand, was reported to be induced by a decrease in the content of

Compared with other developmental processes within the plant, e.g. greening and senescence (refer Section 1.4), re-greening has attracted less attention by researchers. As a result, the evolutionary advantage of re-greening, and how it is induced and controlled, is still largely unknown. The research on spathe re-greening of ‘Best Gold’ presented in this thesis has attempted to fill some gaps in the scientific knowledge of re-greening per se, meanwhile aiming to also address the horticultural

problem caused by re-greening in Zantedeschia (refer Section 1.2).