The in vivo Three-dimensional Form of a Plant Mycoplasma-like Organism by the Analysis of Serial Ultrathin Sections

Abstract

Mycoplasma-like organisms (MLO) associated with lethal yellowing disease of coconut palms exhibited a range of different morphologies even within the same sieve element. The morphologies were revealed by graphic reconstruction from ribbons of serial ultrathin sections containing 45 sections. Five different morphotypes were recognized amongst the 120 organisms reconstructed. MLO could be saccate, erythrocyte-like, cylindrical, moniliform or filiform. The different morphotypes showed differences in linear dimensions apart from their particular morphological characteristics. Saccate MLO were generally the smallest, the maximum length being 1 pm, whilst the filiform organisms could be more than 16 ,um long. The morphologies of the MLO were analogous to those now recognized as usual for Mycoplasma and Acholeplasma species in vitro during the later stages of development. Comparison of the individual profile shapes used in the reconstructions with those of MLO from other diseased plants suggest that many previous interpretations of MLO morphology may have been too simple. With the insight provided by the understanding of the relationship between profile shape and three-dimensional form, the ultrastructure of individual profiles is shown to be an important indicator of form. I N T R O D U C T I O NObservations of intact mycoplasmas taken from culture show that although they occur most frequently as simple spheres or filamentous bodies they are capable of becoming freely branched or even giving rise to mycelial complexes (Razin, 1978;Tully, 1978). Other modifications of form, such as rings and beaded chains, have also been described. The elucidation of morphology in vitro began nearly 70 years ago but the exceptionally detailed light microscopic studies of Turner (1 935) provide some of the best early illustrations. More recently, the use of similar or more sophisticated techniques has generally confirmed these early studies despite some controversy over the manner of reproduction and the significance of the numerous biological and physical factors which are known to affect form (

Efficient elimination of sweetpotato little leaf phytoplasma from sweetpotato by cryotherapy of shoot tips

“…This is particularly important with vegetatively propagated crops in which infected planting materials transmit the pathogen to the new crop. Phytoplasmas are restricted to the phloem (Waters & Hunt, 1980) and colonise meristems poorly (Lee et al ., 2000). Pathogen‐tested plant stocks, in which phytoplasmas have not been detected, have been obtained using many different techniques, such as shoot tip culture (Green et al ., 1989; Wongkaew & Fletcher, 2004; Chalak et al ., 2005), thermotherapy (Kahn et al ., 1972; Green et al ., 1989; Chalak et al ., 2005), leaf tissue‐derived somatic embryogenesis (Parmessur et al ., 2002), organogenesis (Wongkaew & Fletcher, 2004), stem culture (Dai et al ., 1997), micrografting (Chalak et al ., 2005) and treatment of plant tissues with antibiotics (Green et al ., 1989; Davies & Clark, 1994; Wongkaew & Fletcher, 2004).…”

Isolation and Preliminary Characterization of a Spiroplasma from Coconut Palms in Jamaica

“…Such conclusions are not justified at present, and must also be reconciled with the in vivo morphology of lethal yellowing MLO described by Waters & Hunt (1980). These authors found no evidence for spiroplasmal morphology in a detailed analysis of serial ultrathin sections of MLO in sieve elements from lethal yellowing-diseased coconut roots.…”

Coconut and other palm trees

“…However, in most mature tissues, phytoplasma concentrations were found generally below detectable levels (Thomas, 1979, Waters andHunt, 1980). The pathogen could be most readily found in unemerged phloem-rich leaf bases surrounding the apical meristem and, to a lesser extent, in inflorescences and tertiary roots.…”