Don Keiller

Control of carbon partitioning by light quality mediated by phytochrome

Abstract Dry matter distribution, soluble sugar and leaf starch contents, and sucrose phosphate synthetase (SPS) and acid invertase levels were measured in organs of radish (Raphanus sativus L.) plants which had been grown in either white light (WL) or white light plus far-red light (WL + FR). Plants which received additional FR accumulated significantly less dry matter and distributed a greater proportion of this into aerial growth than did controls under WL only. Leaves from plants treated with WL + FR contained 2–3 times as much hexose sugar, lower starch levels and significantly higher SPS activity than plants grown under WL only. The petioles of plants grown in WL + FR contained double the amount of hexose sugar and significantly higher levels of acid invertase activity than those of WL-grown plants. Conversely, the roots of WL + FR plants contained less hexoses and had lower acid invertase activity than WL-grown plants. The results indicate a close relationship between changes in plant growth and morphology in response to altered light quality, mediated via the photoreceptor, phytochrome, and altered enzyme activity in both source and sink organs.

Incidence of the Plateau at V˙O2max is Dependent on the Anaerobic Capacity

The purpose of this study was to address if there is an association between the plateau at V˙O (2max) and the anaerobic capacity. 9 well-trained cyclists (age 22.2 ± 3.5 yr, height 182.5 ± 5.0 cm, mass 75.7 ± 8.7 kg, V˙O (2max) 59.3 ± 4.8 ml x kg(-1) x min(-1)completed both an incremental step test of 20 W x min(-1) starting at 120 W for determination of maximal oxygen uptake (MOU) and a maximally accumulated oxygen deficit (MAOD) trial at 125% MOU for estimation of anaerobic capacity. Throughout all trials expired air was recorded on a breath-by-breath basis. A significant inverse relationship was observed between the MAOD and the Δ V˙O (2) during the final 60 s of the MOU test (r=-0.77, p=0.008). Of the 9 participants it was noted that only 4 exhibited a plateau at MOU. There were non-significant differences for V˙O (2) and the associated secondary criteria for those exhibiting a plateau and the non-plateau responders, despite a significant difference for MAOD (p=0.041) between groups. These data suggest that incidence of the plateau at MOU is dependent on anaerobic substrate metabolism and that ranges of responses reported in the literature may be a consequence of variations in anaerobic capacity amongst participants.

The effects of exercise modality on the incidence of plateau at V·O2max

The purpose of this study was to determine the effect of exercise modality on the incidence of plateau at V·O2max . Twelve recreationally active men (age, 21·7 ± 2·3 year; mass, 74·8 ± 6·5 kg; height, 177·6 ± 5·6 cm) completed four incremental tests to volitional exhaustion, of which two were completed on a treadmill (TRE) and two were completed using a cycle ergometer (CYC). The work rate employed for CYC was 1 W·2 s−1 from an initial loading of 100 W with cadence being maintained at 60 rpm. For TRE, the workload (gradient) increased at a rate of 0·5% · 30 s−1while maintaining a constant running speed of 10 kph. Throughout all the trials, V·O2 was determined on a breath‐by‐breath basis using a precalibrated metabolic cart. The criteria adopted for determination of a plateau was a Δ V·O2 over the final two consecutive 30‐s sampling periods of ≤50 ml · min−1. Averaging across the two trials per each exercise modality showed a significant difference for plateau incidence between CYC (8%) and TRE (58%) (P = 0·017). This was aligned with a significant difference in the slope of the regression line during the final 60 s of the V·O2max test, CYC (99·9 ± 49·7 ml · min−1) and TRE (49·6 ± 42·6 ml · min−1) (P = 0·017). Repeat measures ANOVA of these data suggests that plateau incidence rates at V·O2max differ between treadmill‐ and cycle ergometry‐based exercises. Future studies need to address whether these response rates are replicated in well‐trained athletes.

The incidence of plateau at VO(2max) is affected by a bout of prior-priming exercise.

The purpose of this study was to determine the effect of 6 min of prior‐priming exercise on the incidence of plateau at 2max. Twelve trained cyclists (age, 21 ± 3 years; height, 175·0 ± 8·0 cm; weight, 69·0 ± 10·4 kg; maximal oxygen uptake (2max), 56·3 ± 6·9 ml kg−1 min−1) completed three incremental tests to volitional exhaustion, which were classified as unprimed (UP), heavy‐primed (HP) and severe‐primed (SP), at a work rate of 1 W 2 s−1, from an initial workload of 100 W, for the determination of 2max. 2max trial in the HP and SP conditions was preceded by a period of 4‐min unloaded cycling followed by a further 6 min of constant load cycling at Δ50%2 gas exchange threshold (GET)‐ 2max (HP) and Δ75%2 GET‐2max (SP). Expired air was recorded on a breath‐by‐breath basis during all trials. The criteria adopted for a plateau in2max was a Δ2 over the final two consecutive 30‐s sampling periods ≤2·1 ml kg−1 min−1. There was a significant increase in plateau responses between the UP (50%) and HP (100%) conditions (P = 0·001) coupled with a significant change in the slope of the regression line during the final 60 s of the 2max test, UP and HP (P = 0·0299) and UP and SP (P = 0·0296). These data suggest that a bout of prior‐priming exercise promotes an increased incidence of plateau responses at VO2max. It is suggested that future studies address how such an approach can be adopted without prior knowledge of GET.

The effects of menstrual cycle phase on the development of peak torque under isokinetic conditions

BACKGROUND: There are alterations in strength in relation to menstrual cycle phase but little data attributing these responses to female sex hormone levels using a pseudo-menstrual cycle group as control. OBJECTIVE: Examining the effects of menstrual cycle phase on the development of peak torque across a range of isokinetic speeds. METHOD: 17 well trained females, 11 formed the non-oral contraceptive group (n-OC) (age 20.7 ± 1.4 yrs, mass 59.2 ± 6.9 kg, height 166.8 ± 7.1 cm) and 6 the oral contraceptive control group (OC) (age 20.3 ± 0.5 yrs, mass 60.5 ± 4.2 kg, height 164.8 ± 4.8 cm). Concentric strength of the knee flexors and extensors (60–240°/s) was assessed, corresponding to menstruation (MEN), mid-follicular (mFOL), mid-luteal (mLUT) and pre-menstrual (pMEN). RESULTS: For n-OC significant decreases in peak torque production of the extensors at 120°/s (P=0.0207) (MEN) and of the flexors at 60°/s (P=0.0116) (MEN) and 120°/s (P=0.0282) (MEN) were observed compared to pMEN. No significant differences were observed across any menstrual cycle phase and peak torque for the OC group (p> 0.05). Significant positive correlations were observed (mLUT) between peak torque and oestrogen at 60°/s (P=0.040) and 120°/s (P=0.031). CONCLUSIONS: There are significant fluctuations in peak torque of the knee extensors in response to phases of the menstrual cycle associated with variances in the female sex hormones. The findings have implications for the planning of strength training in female athletes.

Polyclonal antibodies raised to phycocyanins contain components specific for the red-absorbing form of phytochrome.

Polyclonal antibodies raised in rabbits to a mixture of sodium-dodecyl-sulphate-denatured C- and allo-phycocyanin, isolated from Anabaena cylindrica, cross-react with 124-kilodalton (kDa) phytochrome from etiolated oats, in enzyme-linked immunosorbent assays and on Western blots. The component(s) of the anti-phycocyanin serum that cross-reacts with phytochrome appears to be specific for the red-absorbing form of phytochrome (Pr). These antibodies can be detached from Pr by irradiation with red light, and thus show photoreversible binding. This property has been used to immunopurify the anti-phytochrome component from the antiserum using red light as the eluting agent. Competition assays and epitope-mapping studies indicate that the anti-phytochrome component may bind to a site located between 6 and 10 kDa from the amino-terminus of etiolated oat phytochrome.