Leaf Growth Development in Relation to Gas Exchange in Quercus marilandica Muenchh.

Immature leaves ofWeinmannia racemosaare more heat tolerant than mature leaves based on differences in chlorophyllafluorescence and solute leakage

“…1) as well as new chlorophyll synthesis (Hughes et al 2007). The decrease in chlorophyll a/b ratios during leaf expansion (IME compared with IM) has been observed in other species exhibiting green developing leaves (Hughes et al 2007, Manetas et al 2003 and was probably because the chloroplasts in young leaves have underdeveloped thylakoids (Choinski & Wise 1999) with higher amounts of PSII relative to PSI (Pettigrew & Vaughn 1998). The carotenoid/ chlorophyll ratio also decreased during leaf expansion (Table 1), consistent with most (Barker et al 1997;Hughes et al 2007;Krause et al 1995), although not all previous studies (Manetas et al 2002).…”

“…The role of carotenoids in photoprotection through the xanthophyll cycle has been well documented (DemmigAdams & Adams 1998) and so the decreases accompanying leaf expansion are typically associated with increased reflection of photoinhibitory light (Hughes et al 2007) or the development of some structural photoprotective feature (e.g. a thick cuticular layer) (Choinski & Wise 1999). Weinmannia racemosa is likely to be in the latter category because M leaves reflected less visible light than either IM or IME leaves (data not shown), but had thicker cuticles and more developed epidermal layers (Fig.…”

“…Finally, enhanced thermotolerance of young leaves may have ecological importance, particularly in species with extended periods of leaf expansion and/or those that undergo continuous or multiple flushes during the growing season. The literature does not contain extensive information about these points, although for a fast-growing species of Syzygium, full leaf expansion was reached within 7Á10 days after bud break , whereas other species (including W. racemosa) required 20Á35 days to fully expand (Choinski & Wise 1999;Green & Jane 1983;Woodall et al 1998). Many woody species from temperate climates also show multiple flushes during the growing season, including: Syzygium sp.…”

Leaf Trichome Formation and Plant Resistance to Herbivory

“…They may increase tolerance to drought by reducing absorbance of solar radiation and increasing the leaf surface boundary layer (Ehrlinger 1984;Choinski and Wise 1999;Benz and Martin 2006), and by facilitating condensation of air moisture onto the plant surface (Jeffree 1986). Trichomes may further protect living cells from damage caused by solar UV-radiation (Skaltsa et al 1994), and low temperatures .…”

Testing Subspecies Limits in Monardella villosa

“…The longer and more dense trichomes of subsp franciscana could hold the water droplets further away from the leaf surface, allowing for gas exchange to occur through stomata, and increase transpiration. The hairs may also function in UV protection (Choinski and Wise, 1999) and/or creating a boundary layer decreasing the rate of water loss (Ehleringer and Mooney, 1978).…”