Dehiscence of Fruit in Oilseed Rape (Brassica nap us L.): II. THE ROLE OF CELL WALL DEGRADING ENZYMES AND ETHYLENE

Pod shatter in oilseed rape is accompanied by the degradationof the cell wall at the site of fruit dehiscence. Cell separationis preceded by an increase in the activity of the hydrolyticenzyme cellulase (ß 1,4-glucanase, E.C. 3.1.2.4 [EC] ),and this rise in enzyme activity is restricted to the dehiscencezone cells. In contrast, the activity of the cell wall degradingenzyme polygalacturonase (E.C. 3.2.1.15 [EC] ) exhibits no correlationeither temporally or spatially with pod dehiscence. An analysisof the ethylene production profile by intact pods during maturationhas revealed the existence of an ethylene climacteric and thisis temporally correlated with the tissue-specific increase incellulase activity. The major site of ethylene production bythe fruit has been identified to be the developing seed. Sincemaintenance of intact pods in ethylene accelerates both thesenescence and dehiscence of the tissue, it is possible thatthis gaseous regulator plays an important role in the processof pod shatter in vivo. Key words: Oilseed rape, Brassica napus, pod shatter, cellulase, polygalacturonase, ethylene     

Anatomical and Biochemical Changes Associated with the Induction of Oilseed Rape (Brassica napus) Pod Dehiscence by Dasineura brassicae (Winn.)

Dehiscence of pods at an early stage of development is a characteristicof oilseed rape pods damaged by Dasineura brassicae (pod midge).Anatomical examination of pods exhibiting symptoms of infestationrevealed a loss of cohesion between intact cells of the dehiscencezone, a narrow tissue of thin-walled cells present between thevalve margins. Determination of hydrolytic enzyme activity inpericarp tissues of damaged siliquae showed localized enhancementof both polygalacturonase (EC 3.2.1.15 [EC] ) and cellulase (ß1,4 glucanase, EC 3.1.2.4 [EC] ) activity, positionally consistent withthese factors being responsible for the observed cell wall degradation.Mechanistic similarities of midge-induced and maturation-associatedpod dehiscence are discussed. Oilseed rape, Brassica napus L. cv., Bienvenu, pod shatter, pod midge, Dasineura brassicae (Winn.), cellulase, polygalacturonase     

Dehiscence of Fruit in Oilseed Rape (Brassica napus L.): I. ANATOMY OF POD DEHISCENCE

The development sequence of anatomical changes taking placewithin the pericarp tissues of Brassica napus siliquae havebeen studied at a fine- and ultra-structural level. Tissue differentiationoccurred during the initial 20 d after anthesis (DAA) and allowedthe identification of dehiscence zone cells. This descrete tissuewas subsequently further delineated by extensive lignificationof adjacent valve edge and replar vascular cells. Concomitantwith the onset of pericarp lignification, cytoplasmic contentsof the thin-walled dehiscence zone cells exhibited progressivesenescence and degradation. Wall breakdown, initially evidentin pods by 60 DAA, exclusively affected cells within the dehiscencezone, and eventually extended throughout this tissue from theepidermal suture to the locule, thus precipitating valve detachment.Ultrastructural examination confirmed that this loss of cellularcohesion was primarily attributable to middle lamella degradationand, furthermore, the dissolution of wall material was apparentlydependent on rupture of the dehiscence zone protoplast. Thesignificance of dehiscence zone cell modifications in relationto autolytic cell wall breakdown, together with possible implicationsfor the regulation of pod shatter, are discussed. Key words: Oilseed rape, Brassica napus, pod shatter, dehiscence zone, cell wall breakdown     

A TWO LITRE SCALE CONTINUOUS CULTURE APPARATUS FOR MICRO-ORGANISMS

SUMMARY: The design and construction of a continuous culture apparatus with a 2 1. culture vessel are described. Aeration is achieved by means of a mechanical stirrer and injected air, automatic temperature and pH control are features of the apparatus, and foaming is controlled by adding antifoam through a manually operated valve. A high degree of agitation ensures that good mixing takes place. Accurate and easily variable control of the medium flow rate is obtained by means of the Mariotte bottle principle. The apparatus can be operated continuously with freedom from contamination for periods in excess of 1000 hr.