ARL1, a LOB-domain protein required for adventitious root formation in rice

Adventitious roots constitute the bulk of the fibrous root system in cereals. Compared with the current understanding of shoot development, knowledge of the molecular mechanisms of development of the adventitious roots of cereals is limited. We have isolated and characterized a novel gene controlling the initiation of adventitious root primordia in rice (Oryza sativa L.). The gene, designated Adventitious rootless1 (ARL1), encodes a protein with a LATERAL ORGAN BOUNDARIES (LOB) domain. It is expressed in lateral and adventitious root primordia, tiller primordia, vascular tissues, scutellum, and young pedicels. ARL1 is a nuclear protein and can form homodimers. ARL1 is an auxin- and ethylene-responsive gene, and the expression pattern of ARL1 in roots parallels auxin distribution. Our findings suggest that ARL1 is an auxin-responsive factor involved in auxin-mediated cell dedifferentiation, and that it promotes the initial cell division in the pericycle cells adjacent to the peripheral vascular cylinder in the stem.     

太原黄耆(豆科)花器官及胚珠发育研究

太原黄耆是新近发表的物种,分布于中国陕西和山西。该实验利用扫描电子显微镜对太原黄耆的花器官发生和发育过程进行观察研究。结果显示:(1)太原黄耆的各轮花器官都是从远轴端向近轴端单向连续发生,在不同轮之间存在花器官重叠发生的现象。(2)在花的发育过程中,出现2种共同原基,即初级共同原基和次级共同原基,由初级共同原基发育成对萼雄蕊原基和次级共同原基,再由次级共同原基发育成花瓣原基和对瓣雄蕊原基。(3)雄蕊管近轴端基部开口是在进化过程中产生的特殊结构,是一种对传粉者的适应机制,从而有利于传粉活动的进行。(4)胚珠为倒生胚珠,具有2层珠被,认为倒生胚珠是内外2层珠被共同作用的结果。     

氮源浓度对平菇菌丝生长和子实体形成的影响

本文报道了合成培养基中不同氮素水平对平菇菌丝生长和子实体原基产生的影响。平菇菌丝对基质中氮含量的要求较宽。在０．０２８－０．０９３％范围内生长都良好;但缺氮时严重抑制生长,菌丝也不发生扭结。实验结果还表明,硫胺素可能对氮素利用有促进作用,较高的起始氮浓度（０．０４７－０．０９３％）有利于子实体原基的形成。     

Control of root growth: effects of carbohydrates on the extension, branching and rate of respiration of different fractions of wheat roots

Rates of extension, numbers of laterals and rates of respiration were measured in different fractions of wheat ( Triticum aestivum L. cv. Alexandria) roots following changes in carbohydrate supply. The supply of carbohydrate was varied by selective pruning and exogenously fed sugars. Pruning shoots to a single leaf (leaf-pruning) reduced the rate of O₂ uptake by intact roots. Rates were not stimulated by shortterm feeding of sucrose (25 m M ), but were stimulated by the uncoupler p -trifluoro-methoxy(carbonylcyanide)phenylhydrazone (FCCP). Feeding glucose to roots of leaf-pruned and non-pruned plants for 16–24 h increased the rate of O₂ uptake. It is concluded that respiration is under fine control by adenylates and coarse control by carbohydrate supply, with carbohydrates regulating directly the rate of some energy consuming process(es). These energy consuming processes are located in growing tissue fractions. Feeding glucose to leaf-pruned and non-pruned plants increased rates of O₂ uptake in seminal root tips, the zone of developing lateral primordia and mature root sections with elongating laterals, but had no effect on mature sections from which the laterals had been excised. Leaf-pruning reduced the extension rate of seminal axes and first-order laterals when measured over 24 h. Feeding glucose to roots from the time of pruning increased the rate, but did not fully restore it to control values. Pruning roots to a single seminal axis (root-pruning) and feeding glucose to non-pruned plants had no effect on the extension rate of the seminal axis or its laterals over this time period, although rates were increased by root-pruning when measured over 3 days. The number of lateral root primordia was reduced by leaf-pruning and increased by root-pruning and feeding glucose. The results are discussed in terms of the role of carbohydrates in the control of root growth and branching.     

IHH and FGF8 coregulate elongation of digit primordia

In the developing limb bud, digit pattern arises from anterior-posterior (A-P) positional information which is provided by the concentration gradient of SHH. However, the mechanisms of translating early asymmetry into morphological form are still unclear. Here, we examined the ability of IHH and FGF8 signaling to regulate digital chondrogenesis, by implanting protein-loaded beads in the interdigital space singly and in combination. We found that IHH protein induced an elongated digit and that FGF8 protein blocked the terminal phalange formation. Molecular marker analysis showed that IHH expanded Sox9 expression in mesenchymal cells possibly through up-regulated FGF8 expression. Application of both IHH and FGF8 protein induced a large terminal phalange. These results suggest that both enhanced IHH and FGF8 signaling are required for the development of additional cartilage element in limbs. IHH and FGF8 maybe play different roles and act synergistically to promote chondrogenesis during digit primordia elongation.     

Common otolith microstructure related to key early life‐history events in flatfishes identified in the larvae and juveniles of cresthead flounder Pseudopleuronectes schrenki

Otolith microstructure of reared and wild cresthead flounder Pseudopleuronectes schrenki larvae and juveniles was used to investigate the daily periodicity of ring formation, morphological change and unique otolith structure related to important life events. By comparing microstructural features of P. schrenki with those reported for other flatfish species, it was shown that there may be microstructural features that are common to all flatfishes. In the sagittae and lapillus, a check (a distinct ring) was formed in the centre of otoliths at c. 6 days post hatching, and the daily formation of rings observed outside the check was confirmed. During metamorphosis, accessory primordia (AP) of otolith growth were formed on the outer edge of the sagittae, and the shape of the sagittae became more complex. No AP was formed on the lapilli, however, and otolith rings were concentrically formed throughout the larval and juvenile (≤51·6 mm standard length, L_S) stages. It is proposed, therefore, that lapilli are more appropriate than sagittae for analysis throughout the larval and juvenile (≤51·6 mm L_S) stages. During metamorphosis, unique rings that are relatively wide and show weak contrast are formed on lapilli (metamorphosing zone, MZ). Hence, the duration of metamorphosis, larval duration and the days of juvenile life can be estimated by the number of rings within the MZ, using rings from the check to outermost ring of the MZ, and that of rings formed outside MZ, respectively. The formation of AP on sagittae as well as the absence of AP, bilateral asymmetry and the formation of a unique structure during metamorphosis on lapilli have also been reported for other flatfishes.     

In vitro studies on the anatomy and morphology of bud regeneration in melon cotyledons

Summary The anatomy and morphology of bud regeneration were investigated in melon (Cucumis melo L.) cv. Galia, which regenerates in vitro only by direct organogenesis from the cotyledon explant. Explants were cut from the cotyledon proximal to the apex from 3-d-old in vitro seedlings. After 3 d on Murashige and Skoog medium with N⁶-benzyladenine, cell division can be observed in the epidermal layer on the adaxial side in the center of the explant, near the most proximal (wounded) cut edge. Over the next week, the area of the meristem increases laterally. Additional cell layers are added to the meristematic area by cell division in the epidermis. In places the epidermis remains active in cell division. Alongside those active areas there are zones where the epidermis has become inactive, although the subepidermal layers continue to divide. In transverse section, the explant now has small protuberances on the adaxial surface. After 10 d on cytokinin-containing medium, the first signs of development are visible on the adaxial surface adjacent to the proximal cut edge. The protuberances observed after 10 d are neither primordia nor buds, although some meristematic bulges are observed. The first regenerated shoot buds are observed histologically after 15 d, by which time the surface has many protuberances and some small leaves. The first shoot is found by histology after 22 d. By this time the surface is covered with protrusions and leaves, mostly without accompanying buds. The leaves may be produced from the protrusions initially visible after 10 d.     

Cell Death in Cells Overlying Lateral Root Primordia Facilitates Organ Growth in Arabidopsis

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Effects of water deficit stress on the developmental growth of excised tomato roots cultured in vitro

Summary Excised tomato roots (Lycopersicon esculentum Mill. cv Bonny Best) were cultured in the presence of mannitol to determine the effects of varying degrees of mild water deficit on their developmental growth. It was found that over the 7-d culture period, the cultured roots could regulate their own developmental responses to the water deficit such that elongation of the primary root axis was favored over that of the lateral roots. Higher degrees of water deficit proportionately decreased lateral root number and density, but lateral root primordia (visualized by clearing roots in chromium trioxide) continued to be formed in water-stressed roots. Measurements of water and osmotic (solute) potentials of the root tips showed that the cultured roots osmoregulated and did not suffer a loss in turgor pressure as a result of the mannitol treatments. However, reciprocal transfer experiments showed that root cultures were unable to resume growth after removal from water deficit conditions, thus indicating a probable requirement for the shoot for complete recovery.