Christof Godts

Light quality modulates metabolic synchronization over the diel phases of crassulacean acid metabolism

Summary Besides the acknowledged roles of red light, blue light is a key determinant for synchronizing the metabolic and physiological components of CAM over the day/night cycle.

Sedoheptulose accumulation under CO2 enrichment in leaves of Kalanchoë pinnata: a novel mechanism to enhance C and P homeostasis?

In contrast to the well-documented roles of its mono- and bisphosphate esters, the occurrence of free sedoheptulose in plant tissues remains a matter of conjecture. The present work sought to determine the origin of sedoheptulose formation in planta, as well as its physiological importance. Elevated CO2 and sucrose induction experiments were used to study sedoheptulose metabolism in the Crassulacean acid metabolism (CAM) plants Kalanchoë pinnata and Sedum spectabile. Experimental evidence suggested that sedoheptulose is produced from the oxidative pentose phosphate pathway intermediate sedoheptulose-7-phosphate, by a sedoheptulose-7-phosphate phosphatase. Carbon flux through this pathway was stimulated by increased triose-phosphate levels (elevated CO2, compromised sink availability, and sucrose incubation of source leaves) and attenuated by ADP and inorganic phosphate (Pi). The accumulation of free sedoheptulose is proposed to act as a mechanism contributing to both C and P homeostasis by serving as an alternative carbon store under elevated CO2 or a compromised sink capacity to avoid sucrose accumulation, depletion of inorganic phosphate, and suppression of photosynthesis. It remains to be established whether this acclimation-avoiding mechanism is confined to CAM plants, which might be especially vulnerable to Pi imbalances, or whether some C3 and C4 plants also dispose of the genetic capacity to induce and accelerate sedoheptulose synthesis upon CO2 elevation.

Impact of developmental stage on CAM expression and growth in an Aechmea hybrid under greenhouse conditions

Summary Besides environmental factors, expression of crassulacean acid metabolism (CAM) and the related production of malic acid may depend on plant developmental stage. This topic has not yet been investigated under commercial greenhouse conditions. In CAM plant cultivation, malic acid is a central determinant of plant growth, but can also cause physiological leaf damage problems. Here, we present data on diurnal leaf malic acid contents, relative water content dynamics, and measurements of growth at four stages of the plant growth cycle (i.e., ex vitro-acclimated plantlets, 6-month, 12-month, and 18-month-old plants) of Aechmea ‘Maya’. The results obtained showed that Aechmea ‘Maya’ was an obligate CAM plant at all developmental stages during cultivation. Nevertheless, there was some developmental control on the expression of CAM. Under the same environmental conditions, 6-month-old plants accumulated significantly higher amounts of malic acid in their leaves, thus supporting higher growth rates, than in the other growth stages. This larger malic acid pool implied a higher risk of physiological leaf damage, but since remobilisation of malic acid in the early morning remained unaffected during growth, physiological leaf damage might occur throughout vegetative growth.

Impact of fertiliser level on plant growth, plant shape, and physiological leaf damage in two cultivars of Aechmea characterised by crassulacean acid metabolism.

Summary The efficacy of different fertiliser levels was evaluated in terms of plant growth, plant shape, and leaf quality. Experiments were conducted on two cultivars of Aechmea of known sensitivity (high and low, respectively) to physiological leaf damage. Plants were grown under two fertiliser levels (a fertigation solution of 1.2 mS cm−1, or a fertigation solution of 2.4 mS cm−1) over a 9-month treatment period. In general, the lower level of fertiliser resulted in more desirable, compact plants, with leaf length as the major parameter determining plant shape. The higher level of fertiliser improved the growth rate significantly, but also increased the risk of leaf quality problems. The extent of this effect was strongly cultivar-dependent. In practice, growers will have to compromise between plant shape and leaf quality on the one hand, and growth rate on the other. Based on this work, either of two plant-related parameters can be used to evaluate the risk of leaf quality problems when changing fertiliser levels: (i) chlorenchymal cell dimensions at the leaf anatomical level, or (ii) turgor pressure at the leaf physiological level.