The Effect of Supplementary Pollination on Nut Set of Macadamia (Proteaceae)

The effects of supplementary pollination on initial and finalnut set and nut weight of theMacadamia cultivars, ‘HawaiiAgricultural Experiment Station 246’ and ‘HiddenValley A4’, were assessed over 3 years at an orchard ineastern Australia. The final nut sets of racemes bagged to excludeinsect pollinators were low in all 3 years of the study forboth cultivars. This demonstrated the importance of exposureto insect visitors to increase nut set of these cultivars. However,the improved initial nut set by supplementary cross pollinationof 246 in all 3 years of the study showed that insect pollinationis inefficient compared to hand pollination. Furthermore, supplementarycross pollination of 246 increased final nut set by 57–97%in 1989 and increased nut weight by 15.0% and kernel weightby 20.0% in 1991. Cross pollination of A4 did not result inany consistent pattern of initial nut set and did not improvefinal nut set, but increased nut weight by 11.6% and kernelweight by 18.4%, with a higher percentage kernel recovery in1991. In addition, supplementary self pollination of A4 increasednut sets in both 1989 and 1990. Yield and quality of both cultivarsmay benefit from increasing pollen transfer in the orchard. Macadamia integrifolia Maiden and Betche; Macadamia tetraphylla L. A. S. Johnson; macadamia; Proteaceae; cross pollination; self pollination; Apis mellifera ; Trigona ; nut set     

Nitrate Assimilation in Higher Plants with Special Reference to the Cocklebur (Xanthium pennsylvanicum Wallr.)

A soluble NADH-dependent nitrate reductase is described forthe shoot system of Xanthium. Young leaves and immature stemtissues contain high levels of the enzyme. They are relativelyrich in free amino acids and amides but store little free nitrate.The specific activity of the enzyme is lower in fully expandedleaves, although these leaves exhibit higher rates of fixationof carbon in photosynthesis than do younger leaves. Neithernitrate nor free amino acids accumulate in the mesophyll ofthe leaf. Older parts of the stem axis accumulate large amountsof soluble nitrogen, almost entirely as free nitrate. Reservesof nitrate in the shoot and root are rapidly depleted if nitrateis removed from the external medium. Nitrate reductase is apparently absent from roots of Xanthium.This finding is supported by analyses of bleeding sap from nitrate-fedplants which show that 95 per cent of the nitrogen exportedfrom roots is present as free nitrate. However, roots are capableof synthesizing and exporting large amounts of amino nitrogenif supplied with reduced nitrogen such as urea or ammonium. A scheme is presented summarizing the main features of the metabolismof nitrate in Xanthium and this is compared with the situationin nitrate-fed plants of the field pea (Pisum arvense L.), aspecies previously shown to be capable of reducing nitrate inits root system.     

Field Studies of Cereal Leaf Growth: IV. WINTER WHEAT LEAF EXTENSION IN RELATION TO TEMPERATURE AND LEAF WATER STATUS

Throughout winter and early spring, rule and auxanometer measurementsshowed that leaf extension rate (R_E) was directly related totemperature and stopped at about 0°C. During this period,both night and day time R_E responded similarly to temperature.Bright sunshine in late April and May caused fast transpirationwhich was associated with low leaf water potential () and slowR_E. When bright sun was obscured by cloud, R_E increased butthis did not compensate for previous slow R_E. Leaf turgor potential,calculated as the difference between and leaf osmotic potential,was large (0.6–1.8 MPa) and bore little relation to R_E.Low was associated with slower R_E than would have been expectedwithout water stress, but the relation was not unique. On abright day in May, adaptation to low occurred and during theafternoon R_E was faster than at similar values of and meristemtemperatures before noon. The response of R_E and duration ofleaf extension to temperature suggested that for any particularleaf grown under field conditions, variation in mean growingtemperature would affect final leaf length only slightly. Becausesevere water stress slows R_E without affecting the durationof leaf extension markedly, it decreases final leaf size.