The function of regreening in yellow female <i>Leucadendron</i> (Proteaceae)

Abstract

What do female Leucadendron stand to gain by regreening their involucral leaves rather than discarding them after flowering? Regreening of involucral leaves could contribute to the carbon budget and/or protect the developing cone-shaped inflorescence during seed development. This was determined by measuring photosynthesis before anthesis (green involucral leaves), at anthesis (yellow) and after anthesis (regreened) along with photoinhibition (F_v/F_m) and temperature measurements of the floral bracts of exposed and non-exposed inflorescences. The degree of carbon loss or reallocation in response to leaf removal was also determined. Photosynthetic rates of green involucral leaves were only 50% of foliage leaves and removal of involucral leaves did not significantly alter the size or dry weight of the inflorescence. Therefore involucral leaves do not contribute significantly to the overall carbon budget. Although involucral leaves did protect developing cones from photoinhibition and temperature-related bsunburn, there was no significant difference in the severity of final damage between control shoots and shoots where involucral leaves had been removed. Regreening solely for protective purposes is therefore not assumed. The answer to why Leucadendron regreen remains elusive and a more long-term approach is suggested. This work has, however, eliminated the most obvious reasons for the regreening phenomenon.

Keywords: carbohydrate allocation, photoinhibition, photoprotection, regreening

South African Journal of Plant and Soil 2013, 30(3): 147–155