Amelia J. Martyn

Photoinhibition and changes in pigments associated with bract browning in waratahs (Telopea spp., Proteaceae)

Summary The relationship between chronic or long-term photoinhibition, pigment changes, and bract browning in ‘Fire and Brimstone’, ‘Olympic Flame’ and ‘Wirrimbirra White’ waratahs [Telopea speciosissima (Smith) R.Br.] was investigated. Plants were grown under full sun, or under 50% shade-cloth over 2 years, with photoinhibition and pigment changes measured in the bracts and leaves at three stages of floral development (tight bud, juvenile open bud, and mature flower). Photoinhibition of waratah bracts was reduced by shading when applied either from flower initiation in late Summer, or from bud expansion in late Winter, until flower maturity in Spring. Outer bracts showed photoinhibition from the tight bud stage of flower development, and inner bracts from the juvenile open stage, while leaves were not affected. Photoinhibition, measured as pre-dawn photochemical efficiency (PE; Fv/Fm), declined in proportion to bract browning. Bracts on waratah plants kept under shade maintained higher chlorophyll, carotenoid, and anthocyanin levels than bracts exposed to full sun, and thus had a more intense flower colour. A significant decrease in bract pigmentation, combined with photoinhibition, indicates that photodamage occurs in bracts exposed to full sun. Leaf browning did not occur, and waratah leaves maintained a higher chlorophyll concentration than bracts in both full sun and shade conditions. Protection from photoinhibition was correlated with the level of UV-absorbing pigments.