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Bare-root seedlings of Eucalyptus nitens frequently exhibit water stress after planting resulting in leaf lamina damage and reduced leaf area. Two trials examined effects of root exposure and desiccation between lifting and transplanting on post-planting water relations, leaf retention and root growth. Plants with roots exposed on a glasshouse bench initially lost water rapidly. In one trial ψ1 declined to around −2.0 MPa within 2.5 h, after which there was no further change with exposure up to 7.5 h. In the second trial, the initial decline in ψ1 was more rapid, reaching below −2.0 MPa in the first hour, before remaining stable with continuing exposure up to 4.5 h. A further decline then continued to −4.0 MPa after 7.5 h.

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of dairy heifers. Estrus was synchronized in Holstein heifers (estrus = d 0), and heifers then were randomly assigned to either heat stress (n = 10; 33 degrees C, 60% relative humidity) or thermoneutral (n = 11; 21 degrees C, 60% relative humidity) treatment. For heat-stressed heifers, ambient temperature was increased from thermoneutrality to heat stress (33 degrees C) between d 9 and 14 (2.4 degrees C/d increase) after the synchronized estrus and remained between 31 and 33.5 degrees C until d 22. From d 11 to 21, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography, and blood was collected daily for serum progesterone and estradiol analyses. The second wave dominant follicle was larger for the heifers in the thermoneutral environment than for heat-stressed heifers, and ovulation of the second wave dominant follicle occurred in 9 of 11 thermoneutral heifers. For 6 of 10 heat-stressed heifers, the second wave dominant follicle regressed and was replaced by an ovulatory third wave dominant follicle. Smaller follicular size in heat stressed heifers was associated with decreased serum estradiol concentrations between d 11 and 21. Serum concentrations of progesterone during the luteal phase were similar, but luteolysis was delayed in heat-stressed heifers compared with onset in heifers in the thermoneutral treatment. Conclusions were that heat stress inhibited the growth and function of the dominant follicle so that most of the heat-stressed heifers had three follicular waves and a delay in corpus luteum regression.

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29 degrees C, 60% relative humidity) or thermoneutral (n = 11; 19 degrees C, 60% relative humidity) treatment. For cows undergoing heat stress, ambient temperature (19 degrees C) was increased from d 11 to 13 of the estrous cycle (3.3 degrees C/d increase) and remained at 29 degrees C until d 21. Beginning on d 11, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography. Blood was collected daily by coccygeal venipuncture for measurement of serum concentrations of progesterone and estradiol. The second wave dominant follicle was more likely to ovulate in cows in the thermoneutral treatment than in cows undergoing heat stress (91 vs. 18% ovulation, respectively). Patterns of follicular growth in cows under-going heat stress were associated with decreased serum estradiol from d 11 to 21 and on the day of luteolysis. The average day of luteolysis was delayed by 9 d in heat-stressed cows. Conclusions were that follicular growth and development and luteolytic mechanisms were compromised in heat-stressed cows; as a result, luteolysis was delayed, and second wave dominant follicles did not ovulate.

Field symptoms of transplanting shock in Eucalyptus nitens open rooted (1/2 + 1/2) transplants suggest water stress. To identify stages in the development of symptoms, changes in water relations were monitored from undisturbed seedlings growing in a commercial nursery through lifting, transplanting into pots and re-establishment of normal water relations. Hydraulic resistance measured as leaf specific resistivity increased with each step in the transplanting process. Resistivity after lifting was double that measured on undisturbed plants in the nursery and subsequently doubled with each of the two successive stages, root trimming and planting out. Resistivity fell after the initial rise, returning to the values recorded in the nursery in two stages. An initial rapid decrease, which was not accompanied by any measurable root growth, was followed by a seven day period without a change in resistivity before a further gradual decrease as root volume increased with new root growth. All water relations measurements were taken on trees which had not suffered any permanent leaf damage as a result of transplanting. For a small group of trees which did suffer damage there was a significant relationship between root volume at planting and the retained healthy leaf area. Before shoot growth had recommenced the final ratio of turgid leaf area to initial root volume was comparable with plants immediately after lifting and before trimming. The results are discussed in terms of the changes in predawn leaf water potential, leaf water potential and the leaf damage or defoliation symptoms occuring in plantations.

The role of motor innervation in supporting and regulating muscle development was studied using aneural muscles in the hindlimb of the mouse mutant peroneal muscular atrophy (pma). This is a single-locus autosomal mutation where homozygous animals lack the common peroneal nerve, so that muscles in the anterolateral compartment of the lower leg develop entirely without innervation. In adults, these muscles are extremely atrophied, and the mice display a clubfoot deformity. The mutant animals provide a preparation in which aspects of muscle formation can be studied in muscles that have never been exposed to direct contact with somatic motor or sensory axons, without pharmacological or surgical intervention. Using quantitative electron microscopy, we found that normal numbers of primary myotubes formed in aneural pma EDL muscles, but a greater than normal proportion degenerated during the first 2 days after their formation. Secondary myotubes appeared at their normal time and position within the muscle, initially in normal numbers, so that the ratio of secondary to primary myotubes initially was greater in pma than in CF1 control strain mice. No abnormalities in ultrastructure were seen until the time of birth, when retardation in development was obvious, together with invading macrophages and degenerating myofibres. The results show that secondary myotube formation in the mouse, as in the chick (B. J. Fredette and L. T. Landmesser, Dev. Biol. 143, 19-35, 1991) is not directly dependent on innervation. In control muscles, secondary myotubes first form in the vicinity of endplates on primary myotubes. No aggregations of ACh receptors or acetylcholinesterase were present in the aneural muscles, showing that these are neurally induced in the mouse, but secondary myotubes formed in their normal position indicating that positional information related to endplate formation is present in aneural muscles.

Skeletal muscles formed in the absence of innervation are deficient in number of fibers, atrophic, and prone to degeneration. We and others have suggested that primary myotubes form autonomously, and the major effect of embryonic denervation is to halt the formation of secondary myotubes by removing the mitotic stimulus for generation of their precursor myoblasts. This hypothesis has recently been put into question by the results of work by Condon et al. (Dev. Biol., 138, 275-295, 1990) and by B. J. Fredette and L. T. Landmesser (Dev. Biol. 143, 19-35, 1991) who propose that lowered secondary myotube numbers are at least in part due to absence of the primary myotubes which would normally serve as scaffold for their formation. We distinguish between these hypotheses by studying generation and degeneration of primary myotubes and formation of secondary myotubes in fetal rat muscles denervated by injection of beta-bungarotoxin at different times between Embryonic Days (E) 14 and 17. Denervation at any of these times reduced primary myotube numbers on E18 to about 80% of control. Despite this modest decrease in primary myotube numbers, secondary myotube generation fell to below 3% of normal in extensor digitorum longus (EDL) muscles denervated on E14 or E15 and to below 12% of control in soleus muscles denervated on E14-E16. Secondary myotubes were associated with degenerating as well as intact primary myotubes. More secondary myotubes were generated only if nerves had been present up until E16 for EDL or E17 for soleus. We suggest that these observations of a critical period until E16 (EDL) or E17 (soleus) during which innervation is an absolute prerequisite for secondary myotube formation reflect the presence of a nerve-dependent population of myoblasts which must be activated before secondary myotube formation can commence.

Potted blackcurrant plants subjected to moisture stress following harvest produced 50% less total fruit yield in the following season than plants which received regular irrigation. The factors which contributed to this effect were a reduction in the numbers of productive buds, flowers per bud and fruit set. An increase in seed number per fruit in response to the stress suggested that reserve carbohydrates accumulated during the autumn may have been the controlling factor in fruit set. Bud-burst in the stressed plants was both early and uneven, radial growth was reduced, and there was no evidence of starch accumulation at the onset of dormancy. All plants received the same irrigation treatment in the spring following treatment, and there was no significant difference in fruit size except for a few positions at the distal end of the strig. Fruit on stressed plants in this case were the smallest.

A three-year study, combining visual censuses with mist netting and banding, was conducted along a one and a half mile traverse in an area of wet sclerophyll forest in the Brindibella Range, near Canberra. Of the 63 species recorded, 30 per cent. were casual visitors, and one species was a winter resident. A total of 1,720 birds and 35 species was banded, of which 426 (25%) were retrapped, and 206 (12%) were retaken in a subsequent breeding season. The avifauna of the region area studied is strikingly similar to that of the upper Snowy River region in Victoria, and it is suggested that, ecologically, there is little or no gap between the two.

Summary SLX4, a scaffold for structure-specific DNA repair nucleases, is important for several types of DNA repair. Many repair proteins bind to sites of DNA damage, resulting in subnuclear “foci,” but SLX4 forms foci in human cells even without DNA damage. Using several approaches, we show that most, but not all, SLX4 foci localize to telomeres in a range of human cell lines irrespective of the mechanisms used to maintain telomere length. The SLX1 Holliday-junction-processing enzyme is recruited to telomeres by SLX4, and SLX4, in turn, is recruited by a motif that binds to the shelterin subunit TRF2 directly. We also show that TRF2-dependent recruitment of SLX4 prevents telomere damage. Furthermore, SLX4 prevents telomere lengthening and fragility in a manner that appears to be independent of telomere association. These findings reveal that SLX4 plays multiple roles in regulating telomere homeostasis., Graphical Abstract, Highlights • The SLX4 DNA repair complex binds to telomeres in different human cell lines • The SLX4 scaffold protein has a TRF2-binding motif responsible for telomere localization • SLX4 also has localization-independent roles at telomeres, SLX4 is a scaffold protein that regulates several DNA repair endonucleases and forms subnuclear foci in human cells that Rouse and colleagues identify as telomeres. SLX4 is recruited to telomeres by a motif that interacts with the shelterin subunit TRF2. Mutations in this motif prevent SLX4 from localizing at telomeres and cause telomeric DNA damage in human cells. SLX4 also has localization-independent roles at telomeres, such as preventing telomere overlengthening.

Rats fed a restricted diet during gestation and lactation gave birth to pups with about 60 % the normal birthweight. Maintaining the undernutrition after birth reduced the rate of growth of the pups so that their body weights were only 40 % of control at PN7. Soleus and lumbrical muscles in these animals had reduced numbers of muscle fibres, and quantitative examination of embryonic muscles revealed that this was due solely to a decreased formation of secondary myotubes; the number of primary myotubes remained normal. Undernutrition did not affect the number of motoneurones surviving normal developmental death. Restoration of normal dietary intake on E21, one day before birth, did not correct the deficit in muscle fibre numbers in soleus muscles examined when the animals reached one month of age. Development of the lumbrical muscle lags behind the soleus and unrestricted feeding from E21 onwards allowed a normal number of fibres to develop from this time on, although the initial deficit was never restored. These experiments define a critical period in muscle development during which the potential maximum number of secondary myotubes is determined.