The Relationship of Root System with the Growth and Development of Bulbs and Shoots in Lilies

Liliaceae Lilium is one of the most famous flower bulbs in the world. The root system bridges substance exchange between the soil and shoot and a strong root system supports the shoot growth and development. During growth, lilies develop two root systems: the basal root system and the stem root system. A few studies have currently reported the relationship between the growth of lily roots and shoots. In our study, we carried out a growth observation of lily shoots (stem and leaves) and underground parts (bulb, basal roots, and stem roots) by cutting the basal roots, stem roots and bulbs of lily. We also discussed how these treatments affected the growth of lilies. The results indicated that both bulb weight and bulb volume showed an initial decreasing and a subsequent increasing trend during growth, and the bulb weight could better reflect bulb nutrient dynamics compared with the bulb volume. The trend in bulb weight was the opposite to that of shoot weight; the bulb weight decreased at first and then increased, whereas the shoot weight first increased and decreased afterward. The turning points for both variations occurred just at the time of flowering. The variation of plant heights showed a typical S-curve and the time where plant heights entered rapid growth coincided with the time where the stem root system started to emerge. The stem root system only took 10 days to complete development. The biological significance was that after plantation, nutrients supporting the growth of the shoots is mainly supplied and maintained by the bulbs and they should be transferred to the stem roots in the shortest delay possible. During early emergence of the stem root system, substance consumed from the bulb are mainly used for the formation of stem roots and after the number of leaves has become stable, substances supplying the shoot growth are mainly from soil nutrients absorbed by the stem roots. The stem root system plays a key role in the growth and development of lily shoots, whereas the basal roots and the bulb would not affect lily growth to a significant level.

Differences in tissue concentrations of hydrogen peroxide in the roots and cotyledons of annual and perennial species of flax (Linum)

Short-lived annuals should allocate more resources towards reproduction, whereas long-lived perennials should allocate more resources towards tissue maintenance. Although ecological data support this hypothesis, no studies have examined the physiological basis for lifespan differences between annuals and perennials. Based on the oxidative theory of aging, hydrogen peroxide (H2O2) levels should be lower in perennating tissues (e.g., basal roots) — but not nonperennating tissues (e.g., cotyledons) — from perennials compared with annuals. We tested this prediction using two annual and two perennial species of flax ( Linum ). As predicted, H2O2 concentrations were lower in roots from perennials than from annuals, reflecting higher catalase activity in roots from perennials. In cotyledons, contrary to our predictions, H2O2 concentrations were actually higher in perennials than in annuals, despite higher catalase activity in perennials as well, likely reflecting higher H2O2 production via peroxisomes and chloroplasts. Therefore, we propose that, consistent with the oxidative theory of aging, perennial flax species have a lower oxidative burden in their roots, but this comes at the cost of a greater oxidative burden in their shoots. As we demonstrate, perenniality is ancestral in Linum, and so derivation of the annual condition likely involved a physiological shift towards a more equitable oxidative burden between roots and shoots.

Clonal Variation in Lateral and Basal Rooting of Populus Irrigated with Landfill Leachate

Successful establishment and productivity ofPopulusdepends upon adventitious rooting from: 1)lateral rootsthat develop from either preformed or induced primordia and 2)basal rootsthat differentiate from callus at the base of the cutting in response to wounding. Information is needed for phytotechnologies about the degree to whichPopulusadventitious rooting is controlled by effects of individual genotypes, waste waters used as alternative fertigation sources, and their interactions. Our objective was to irrigate twelvePopulusclones with well water (control) or municipal solid waste landfill leachate and to test for differences between initiation of lateral versus basal roots, as well as root growth rate and distributional trends for both root types. We evaluated number and length of lateral roots initiated from upper, middle, and lower thirds of the cutting, as well as basal callus roots. Overall, leachate irrigation affected lateral roots but not basal roots, and there was broad clonal variation between and within root types. On average, there were 129% more lateral than basal roots, which ranged from 3 to 27 (lateral) and 2 to 10 roots (basal). The percent advantage of number of roots from the middle portion of the cutting relative to other sections was 120% (upper), 193% (lower), and 24% (basal). Clones, treatments, and their interaction did not affect root growth rate, which ranged from 1.5 ± 0.6 to 3.4 ± 0.3 cm d−1, with a mean of 2.3 ± 0.2 cm d−1. These results contribute baseline information for clonal selection needed to establishPopulusfor phytotechnologies, energy, and fiber.

Root traits of common bean genotypes used in breeding programs for disease resistance

The objective of this work was to assess root traits of 19 common bean genotypes, used in breeding programs for disease resistance. Genotypes DOR 364 and G 19833 were used as deep and shallow basal root checks, respectively. The number of whorls and basal roots were assessed on five-day old seedlings grown in germination paper. Growth pouch studies were conducted to evaluate basal root gravitropism and lateral root length from primary roots, in seven-day old seedlings. The following root gravitropic traits were estimated: basal growth angle, shallow basal root length (localized in the top 2 cm), and relative shallow basal root growth. Number of whorls varied from 1.47 to 3.07, and number of basal roots ranged from 5.67 (genotype TO) to 12.07 (cultivar Jalo MG-65). Cultivars BRS MG Talismã, Carioca, BRS Pioneiro, and Diamante Negro exhibited shallow basal roots, while genotypes Vi-10-2-1, TU, AB 136, and México 54 showed deep basal roots. Cultivar Jalo MG-65 showed more lateral roots from the primary root than the other genotypes. Genotypes used on common bean breeding programs for disease resistance have great variability on basal and primary root traits.

Ethylene modulates genetic, positional, and nutritional regulation of root plagiogravitropism

Plagiogravitropic growth of roots strongly affects root architecture and topsoil exploration, which are important for the acquisition of water and nutrients. Here we show that basal roots of Phaseolus vulgaris L. develop from 2–3 definable whorls at the root–shoot interface and exhibit position-dependent plagiogravitropic growth. The whorl closest to the shoot produces the shallowest roots, and lower whorls produce deeper roots. Genotypes vary in both the average growth angles of roots within whorls and the range of growth angles, i.e. the difference between the shallowest and deepest basal roots within a root system. Since ethylene has been implicated in both gravitropic and edaphic stress responses, we studied the role of ethylene and its interaction with phosphorus availability in regulating growth angles of genotypes with shallow or deep basal roots. There was a weak correlation between growth angle and ethylene production in the basal rooting zone, but ethylene sensitivity was strongly correlated with growth angle. Basal roots emerging from the uppermost whorl were more responsive to ethylene treatment than the lower-most whorl, displaying shallower angles and inhibition of growth. Ethylene sensitivity is greater for shallow than for deep genotypes and for plants grown with low phosphorus compared with those supplied with high phosphorus. Ethylene exposure increased the range of angles, although deep genotypes grown in low phosphorus were less affected. Our results identify basal root whorl number as a novel architectural trait, and show that ethylene mediates regulation of growth angle by position of origin, genotype and phosphorus availability.

Genetic variation for adventitious rooting in response to low phosphorus availability: potential utility for phosphorusacquisition from stratified soils

We hypothesized that adventitious roots may improve crop adaptation to low-phosphorus soils by enhancing topsoil foraging. In a tropical field study, phosphorus stress stimulated adventitious rooting in two phosphorus-efficient genotypes of common bean (Phaseolus vulgaris L.) but not in two phosphorus-inefficient genotypes. Although phosphorus availability had no consistent effects on the length or biomass of whole root systems, it had differential effects on adventitious, basal, and taproots within root systems in a genotype-dependent manner, resulting in increased allocation to adventitious roots in efficient genotypes. Adventitious roots had greater length per unit biomass than other root types, especially under phosphorus stress. Adventitious roots had less construction cost than basal roots, despite having similar tissue nitrogen content. Phosphorus stress reduced lateral root density, and adventitious roots had less lateral root density than basal roots. Lateral roots formed further from the root tip in adventitious roots compared with basal roots, especially under phosphorus stress. Field results were confirmed in controlled environments in solid and liquid media. Stimulation of adventitious rooting by phosphorus stress tended to be greater in wild genotypes than in cultivated genotypes. We propose that adventitious rooting is a useful adaptation to low phosphorus availability, because adventitious roots explore topsoil horizons more efficiently than other root types.