Variations in the most abundant types of glucosinolates found in the leaves of baby leaf rocket under typical commercial conditions.

BACKGROUND: Changes in the concentration of the three most abundant glucosinolates were measured in the leaves of perennial wall rocket [Diplotaxis tenuifolia (L.) DC.], and annual garden rocket (Eruca sativa Mill.). HPLC-MS was used to identify glucoraphanin, 4-hydroxyglucobrassin and glucoerucin from perennial wall rocket, and glucoraphanin, glucobrassicin and 4-methoxyglucobrassicin from annual garden rocket. In separate experiments the responses of glucosinolates to harvest number, seasonal conditions, nitrogen supply and post-harvest storage conditions were measured. RESULTS: For perennial wall rocket, season influenced the concentration of glucoraphanin, which were highest for the spring [379 µg kg(-1) fresh weight (FW)] and summer (317 µg kg(-1) FW) plantings. The concentration of 4-hydroxyglucobrassin was higher in the leaves of first harvest crops. This response was due to this glucosinolate not being detected in the leaves of second harvest crops. Thus, the parent glucosinolate was altered between the first and second harvests in response to the abiotic stresses caused by harvesting. For annual garden rocket, there was an interaction between the harvest number and season for all glucosinolates measured. However, no clear response was observed between these factors. Higher concentrations of glucobrassicin and 4-methoxyglucobrassicin were measured for first harvest leaves when compared to the second harvest. This was due to the absence of detection of these glucosinolates in the leaves of second harvested plants; consequently higher total glucosinolate concentrations were measured for the first harvest winter (1224 µg kg(-1) FW) and summer (864 µg kg(-1) FW) crops. CONCLUSION: The concentrations of individual glucosinolates vary greatly over typical pre- and post-harvest commercial conditions. The absence of 4-hydroxyglucobrassin for perennial wall rocket, and glucobrassicin and 4-methoxyglucobrassicin for annual garden rocket between harvests, illustrates that abiotic stress from harvesting has the capacity to alter the types of glucosinolates in leaves. Concentrations do not generally decline during a typical storage period, indicating that the potential benefits of these compounds are not lost during post-harvest storage.

Canopy development and hydraulic function in Eucalyptus tereticornis grown in drought in CO2-enriched atmospheres.

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO2 levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30-50% below field capacity), while atmospheric CO2 was raised to 700 µL CO2 L-1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO2 stimulated shoot growth rates for 12-15 weeks in well-watered trees but after six months of CO2 enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO2 sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO2 enrichment. In spite of larger transpiring canopies, CO2 enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO2 on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased.