Characteristic Diel Cycles of Leaf Growth Activity

Leaves of all investigated species show characteristic diel cycles of growth activity under all reported environmental conditions (for a review see Walter and Schurr 2005; or Matsubara and Walter 2006). The intensity and the finestructure of the diel variation varies from day to day and the phasing clearly differs between species (Fig. 3): Leaves of Ricinus communis (Walter et al. 2002a), Nicotiana tabacum (Walter and Schurr 2005) and Arabidopsis thaliana (Wiese et al. 2007) for example showed maximal growth activity in the beginning of the day. These species were also following the classical pattern of base-tip distribution of growth rate with higher growth rates at the leaf base and lower growth rates at the tip. An exactly contrasting phase behavior was displayed by leaves of Populus deltoides (Walter et al. 2005; Matsubara et al. 2006). Here, maximal growth activity was found at the end of the day; growth rate decreased throughout the entire night and

Fig. 3 Diel leaf growth cycles for some dicotyledonous plant species and typical examples for color-coded distribution of relative growth rate (RGR) across the leaf lamina. In high light conditions, Chamecyparis obtusa leaves shrink in the morning. This figure is a reproduction of Fig. 1 in Matsubara and Walter (2006) and is printed with kind permission of Springer Science and Business Media

Fig. 3 Diel leaf growth cycles for some dicotyledonous plant species and typical examples for color-coded distribution of relative growth rate (RGR) across the leaf lamina. In high light conditions, Chamecyparis obtusa leaves shrink in the morning. This figure is a reproduction of Fig. 1 in Matsubara and Walter (2006) and is printed with kind permission of Springer Science and Business Media increased continually throughout the day. The growth behavior of Glycine max is largely comparable, with a somewhat later occurrence of the growth rate maximum (Ainsworth et al. 2005). Interestingly, those two species did not show a base-tip gradient. For leaves of Populus deltoides it was shown by microarray analysis that the nocturnal decrease of growth rates was correlated with a downregulation of genes encoding ribosomal proteins and histones, indicating a decrease of cytoplasmic growth (Matsubara et al. 2006). The investigated species of Populus retains cell division activity within leaves practically until they reach full size (Van Volkenburgh and Talor 1996), while leaves ofRicinus communis (Roggatz et al. 1999) and Nicotiana tabacum (Walter et al. 2003b) merely show cell expansion in post-emergent growth stages. These results support the hypothesis that the difference in phasing of the two growth types might be induced by the differential extent to which leaf growth is driven by cytoplasmic (connected to cell division) and vacuolar (connected to cell expansion) growth.

Diel leaf growth cycles have also been monitored in scale leaves of the gymnosperm species Chamaecyparis obtusa and Chamaecyparis formosensis. Here, maxima of growth activity were recorded at the end of the day or beginning of the night—as in Populus deltoides and Glycine max. Yet, in the two Chamaecyparis species, growth activity was almost constant throughout the night and a base-tip gradient of growth was recorded (Lai et al. 2005). Moreover, significant shrinking of the foliage was recorded in Chamaecyparis when light intensity was increased at the beginning of the day, demonstrating that growth in this gymnosperm genus might be restricted by other factors as in the above mentioned angiosperm species.

A third mode of diel leaf growth activity was recorded in four different species of CAM-plants (Gouws et al. 2005): Leaves of Kalanchoe beharen-sis, Opuntia oricola, Opuntia phaeacantha and Opuntia engelmanii showed growth maxima in the middle of the day, if plants were exposed to low water availability. The maximum of growth activity was correlated with phase III of the crassulacean acid metabolism, in which CO2-fixation via RubisCO is taking place with stomata closed and CO2 gained from malate metabolized at night and stored in the vacuole. The cellular status in this phase of CAM is providing excellent conditions for growth since the availability of carbohydrates is high, cytoplasmic pH is low and turgor is maximal. In C4-plants, the middle of the day also is indicated to be the preferred phase of growth (Watts 1974; Christ 1978; Seneweera et al. 1995).

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