Leaf Blackening/Post Harvest Storage

Jones, R B; Clayton-Greene, K A.
The role of photosynthesis and oxidative reactions in leaf blackening of Protea neriifolia R. Br. leaves.
Scientia Horticulturae (Amsterdam), v.50, n.1-2, 1992:137-145
Abstract: A series of experiments with Protea neriifolia R. Br. found evidence
that leaf blackening is associated with the inhibition of photosynthesis and
its resultant effect on oxidative metabolism. Leaf blackening was
significantly reduced by constant illumination greater than 25 .mu.mol m-2s-1.
The light compensation point for P. neriifolia leaves was estimated to be 24
..mu.mol m-2s-1. Treatment of cut stems with 100 .mu.M
3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of electron
transport in Photosystem II, increased leaf blackening, indicating the
necessity of active photosynthesis in the control of blackening. The nature of
the oxidative processes resulting in blackening was examined. Dipping P.
neriifolia stems in an anti-oxidant (diphenylamine, 1.5 mg l-1) resulted in a
significant reduction in leaf blackening after 7 days. Storage in a low
oxygen, controlled atmosphere (1% O2, 5% CO2) provided effective control
against leaf blackening for up to 14 days at 25.degree. C. It is proposed that
leaf blackening in P. neriifolia leaves is inhibited by active photosynthesis,
possibly through the production of carbohydrates as well as anti-oxidant or
reducing compounds.

Bieleski, R L; Ripperda, J; Newman, J P; Reid, M S.
Carbohydrate changes and leaf blackening in cut flower stems of Protea eximia.
Journal of the American Society for Horticultural Science, v.117, n.1, 1992:124-127
Abstract: We tested the hypothesis that premature leaf blackening in cut
flower stems of Protea eximia (Salisb. ex Knight) Fourcade may be brought
about by a low leaf carbohydrate status. Leaves on cut flower stems held in
darkness blackened within 4 days, whereas those on stems held in a greenhouse
remained healthy for 5 days. Leaf blackening was also retarded by supplying 1%
sucrose in the vase solution; but other additives (hypochlorite, silver
thiosulfate, bisulfite) were not effective. The hypothesis was further
explored by examining postharvest carbohydrate changes in the leaf of cut
flower stems held in light or darkness. At harvest, leaves contained very
little hexose (< 1 mg .center dot. g-1 fresh weight), comparatively small
concentrations of sucrose (.approximateseq. 5 mg .center dot. g-1 fresh
weight) and starch (.approximateseq. 6 mg .center dot. g-1 fresh weight), but
high concentrations (.approximateseq. 30 mg .center dot. g-1 fresh weight) of
the polyol polygalatol. Starch and sugar contents of leaves held in darkness
fell rapidly, to one-third of their initial level after only 1 day and to
one-sixth after 3 days. In contrast, starch and sugar contents increased
slowly in leaves of stems held in light to three times the initial level after
3 days. Polygalatol content was unaffected by any treatment. Removal of the
inflorescence did not delay blackening of leaves held in darkness and did not
affect their carbohydrate changes.

Mcconchie, R; Lang, N S; Cross, K C.
Carbohydrate depletion and leaf blackening in Protea neriifolia.
Journal of the American Society for Horticultural Science, v.116, n.6, 1991:1019-1024
Abstract: Leaf blackening on cut flower Protea neriifolia R. Br. stems was
dramatically reduced under a 12-hour photosynthetic light period (120 .mu.mol
..center dot. m-2 .center dot. s-1) at 25 C for 15 days compared with stems
kept in the dark. In the light, addition of 0.5% exogenous sugar to the vase
solution resulted in a maximum of 2.5% leaf blackening, while stems with no
exogenous sugar had a maximum of 16.5%. Continous darkness resulted in 94%
leaf blackening by day 7, irrespective of sugar treatment. Starch and sucrose
concentrations were markedly lower in leaves on darkheld stems than in leaves
on stems held in the light; thus, carbohydrate depletion could be the primary
stress that initiates leaf blackening. In the light, rates of carbon exchange
and assimilate export were similar, indicating that the amount of carbon fixed
may be regulated by sink demand. The pattern of carbon partitioning changed in
lightheld leaves of the 0% sugar treatment during rapid floral expansion and
senescence. Inflorescence expansion appears to influence partitioning of
photoassimilates and storage reserves into transport carbohydrates; under
decreased sink demand, the assimilate export rate decreases and
photoassimilates are partitioned into starch. The data suggest that sink
strength of inflorescences held in darkness may be responsible for the
depletion of leaf carbohydrates and, consequently, blackening.

Jones, R; Faragher, J.
Cold storage of selected members of the proteaceae and Australian native cut flowers.
Hortscience, v.26, n.11, 1991:1395-1397
Abstract: Five members of the Proteaceae and 13 Australian native cut flower
cultivars were stored for 35 days under standard conditions at 1C to assess
their ability to withstand long-term storage and transport. Protea cynaroides
L., Leucandendron 'Silvan Red', Leucospermum 'Firewheel', Thyrptomene calycina
(Lindl.) Stapf., Telopea speciosissima R. Br., and Verticordia grandiflora
Endl. retained a vase life of at least 7 days after 21 days of storage.
Leucospermum cordifolium Salisb. ex Knight, Protea neriifolia R. Br.,
Chamelaucium uncinatum 'alba',C. uncinatum 'Purple Pride', Vertiordis
monadelpha Turcz., Verticordia plumosa (Desf.) Druce, and Verticordia nitens
(Lindl.) Schau. suffered a decline in vase life ranging from 31% to 100% after
14 to 21 days of storage. Species of Verticordia and Chamelaucium were
particularly susceptible to fungal infection. Anigozanthos pulcherrimus Hook.
and the Anigozanthos cultivars Ruby Delight, Bush Harmony, Bush Haze, and Gold
Fever all showed a significant reduction in vase life after 14 days of storage
compared with unstored controls.

Perold, G W; Carlton, L.
Neriifolin, an ester glucoside of benzene-1,2,4-triol.
Journal of the Chemical Society Perkin Transactions I,n.7, 1989:1215-1218
Abstract: Neriifolin, a leaf metabolite of Protea neriifolia R, Br., is the
6-O-benzoyl-.beta.-D-glucopyranoside of benzene-1,2,4-triol. The location of
the benzoyloxy group on the sugar was directly confirmed by n.m.r.
spectroscopy; the position of the glycosidic linkage to the benzenetriol was
demonstrated by methylation and hydrolysis to 2,4-dimethoxyphenol
(characterised by n.m.r. spectroscopy and by benzoylation).

McConchie, Robyn; Lang, N. Suzanne.
Postharvest leaf blackening and preharvest carbohydrate status in three Protea species.
Hortscience, v.28, n.4, 1993.:313-316.
Abstract: Protea neriifolia R. Br., P. susannae E.P. Phillips x compacta
R.Br., and P. eximia (Salis. ex Knight) Fourcade cut flower stems were
examined to determine the relationship between postharvest leaf blackening
rate and preharvest carbohydrate status. Postharvest leaf blackening was
highest (83% by day 4) in P. eximia floral stems, which had the lowest
preharvest sucrose concentrations. In contrast, P. susannae x compacta had lt
5% leaf blackening by day 4 and the highest preharvest leaf sucrose
concentrations. Starch concentrations were highest in P. neriifolia; however,
leaf blackening was intermediate between P. susannae x compacta and P. eximia
and reached 52% at day 4. Preharvest carbon-exchange rate and stomatal
conductance in all three species were extremely low, despite high
photosynthetically active radiation and apparent lack of water stress.
Comparing preharvest carbohydrate profiles in vegetative and floral stems
suggests that vegetative stems may have a sink-to-source transition zone
between the second and third divisions, while most leaves on floral stems may
have transferred carbohydrates to source leaves at harvest. While preharvest
floral stem sucrose concentrations can be linked to leaf blackening rate, the
high starch reserves in P. neriifolia reduced leaf blackening little in this
species. We conclude that leaf blackening may be related more to inflorescence
sink demand after harvest and oxidative substrate availability than preharvest
reserve carbohydrate concentrations in each species.

McConchie, Robyn; Lang, N. Suzanne.
Carbohydrate metabolism and possible mechanisms of leaf blackening in Protea neriifolia under dark
postharvest conditions.

Journal of the American Society for Horticultural Science, v.118, n.3, 1993.:355-361.
Abstract: During a 7-day dark postharvest period, Protea neriifolia R. Br.
leaf blackening was significantly reduced on floral stems treated with a 24-h
20% sucrose pulse compared with continuous holding in a 0.5% sucrose vase
solution or removal of the flowerhead. Leaf blackening on vegetative stems was
similar to that on the 20% sucrose-pulsed floral stems. Leaf starch and
sucrose concentration profiles demonstrated that stems with reduced leaf
blackening maintained higher levels of those carbohydrates during the early
postharvest period. Conversely, leaf starch and sucrose reserves were quickly
depleted in, stem treatments that resulted in early blackening symptoms.
Starch concentrations in all treatments of stems dropped 70% to 82% within 24
h of harvest, suggesting that leaf blackening may be initiated during
shipping. Ethylene production was not associated with leaf blackening in any
treatment. Lipid peroxidation did not differ among floral treatments nor did
it increase over the postharvest interval. Oxidized glutathione (GSSG)
concentration increased only with the 20% pulsed stems and was not related to
leaf blackening. After an initial decrease, leaf respiration rate was
generally maintained regardless of treatment. Collectively, these data are
consistent with the hypothesis that carbohydrate depletion is the initiating
factor in leaf blackening and is accelerated by inflorescence sink demand. We
suggest that membrane degradation does not necessarily precede leaf blackening.


JOURNAL. Karunaratne, Chinthaka; Moore, Graham A.; Jones, Rodney B.; Ryan,
Robert F.. Vase life of some cut flowers following fumigation with phosphine.
Hortscience, v.32, n.5, 1997.:900-902.
Language: English; Pub type: JOURNAL ARTICLE
Abstract: Phosphine (PH-3) is a potential alternative fumigant to methyl
bromide for insect disinfestation of cut flowers. King protea (Protea
cynaroides L.), tulip (Tulipa gesneriana 'Apeldoorn'), kangaroo paw
(Anigozanthos manglesii Hook.), and geraldton wax (Chamelaucium uncinatum'
Purple Pride') were fumigated with PH, at varying concentrations (100 to 8000
mu-L center dot L-1) for 2,4, or 6 hours. Vase life was evaluated at 20 degree
C, 65% relative humidity, and constant illumination with a photosynthetically
active radiation of 15 mu-mol center dot m-2 center dot s-1. No significant
change in vase life was observed for kangaroo paws after any of the PH-3
fumigations. A 6-hour fumigation at 8000 mu-L center dot L-1 significantly
reduced vase life in king protea, tulip, and geraldton wax flower. Geraldton
wax flower and tulip were relatively sensitive to PH-3, as they were damaged
by 4000 mu-L center dot L-1 for 6 hours and 8000 mu-L center dot L-1 for 4
hours, respectively. Phosphine has potential as an insect disinfestation
fumigant for king protea, tulip, and kangaroo paw at 4000 mu-L center dot L-1
for 6 hours without affecting vase life or causing damage.